A comparison between nuclear dismantling during plant and animal programmed cell death

1 A compa ison be ween nuclea disman ling du ing plan and animal p og ammed cell dea h Fe nando Domínguez and F ancisco Ja ie Cejudo Ins i u o de Bioquímica Vege al y Fo osín esis, Uni e sidad de Se illa and CSIC, A da Amé ico Vespucio 49, 41092-Se illa, Spain Co espondence o: F ancisco Ja ie Cejudo; Ins i u o de Bioquímica Vege al y Fo osín esis, Uni e sidad de Se illa and CSIC, A da Amé ico Vespucio 49, 41092- Se illa, Spain; E-mail: [email p o ec ed] Key wo ds: apop osis, plan , p og ammed cell dea h, nuclease, nucleus disman ling 2 Abs ac P og ammed cell dea h (PCD) is a p ocess o o ganized des uc ion o cells, essen ial o he de elopmen and main enance o cellula homeos asis o mul icellula o ganisms. Cells unde going PCD begin a degene a i e p ocess in esponse o in e nal o ex e nal signals, whe eby he nucleus becomes one o he a ge s. The p ocess o nucleus disman ling includes e en s a ec ing he nuclea en elope, such as o ma ion o lobes a he nuclea su ace, selec i e p o eolysis o nucleopo ins and nuclea po e complex clus e ing. In addi ion, ch oma in condensa ion inc eases in coo dina ion wi h DNA agmen a ion. These p ocesses ha e been la gely s udied in animals, bu emain poo ly unde s ood in plan s. The o e all p ocess o cell dea h has di e en mo phological and biochemical ea u es in plan s and animals. Howe e , ecen ad ances sugges ha nuclea disman ling in plan cells p og esses wi h mo phological and biochemical cha ac e is ics simila o hose in apop o ic animal cells. In his e iew, we summa ize nucleus disman ling in plan PCD, ocusing on he simila i ies and di e ences wi h hei animal coun e pa s. 3 Con en s 1. In oduc ion 2. An o e iew o nuclea disman ling in animal cells 3. Simila i ies in nuclea disman ling in animal and plan cells unde going PCD 3.1. Signalling ha commi s nuclea disman ling in plan s 3.2. Sequence o e en s o plan nuclea disman ling du ing PCD 3.3. Nuclea disman ling is connec ed wi h cy oplasmic e en s du ing plan PCD 4. Is nuclea disman ling an au ophagic p ocess? 5. Concluding ema ks and u u e pe spec i es Acknowledgemen s Re e ences 4 1. In oduc ion P og ammed cell dea h (PCD) is a p ocess o o ganized des uc ion o cells ha main ains cellula homeos asis and is essen ial o he success ul de elopmen o mul icellula o ganisms [1]. PCD is an impo an p ocess in plan s, as in o he mul icellula o ganisms, no only o de elopmen [2], bu also as a mechanism o immuni y agains pa hogen a ack [3]. Plan de elopmen al cell dea h a ec s o de e mined cell ypes a p ecise s ages o de elopmen and is cha ac e ized by he up u e o he acuola onoplas and subsequen elease o hyd olases, which deg ade he cellula con en and, in some cases, he cell wall. Cell dea h in bio ic s ess depends o he ype o pa hogens, bu ee adicals seem o exe an impo an unc ion [4]. The plan cell has peculia cha ac e is ics, mos no ably he p esence o he cell wall and acuoles, which sugges ha he p ocess o PCD akes place wi h di e en mo phological ea u es om apop osis o animal cells. Indeed, mos o he mo phological ea u es o mammalian apop osis a e no ound in plan cells unde going PCD and, hus, i has been p oposed ha cell dea h in plan s does no ake place by he p ocess o apop osis; howe e , he deg ee o conse a ion o plan and animal cell dea h p og ammes is a he momen a ma e o deba e [4]. The no ion ha plan s seem o ha e e ol ed di e en mechanisms o PCD is ein o ced by he biochemical analyses o he componen s in ol ed in he execu ion o cell dea h in di e en plan sys ems. Despi e in ense sea ch, caspases ha e no been ound in plan s whe eas hey a e he mos cha ac e is ic p o eases execu ing apop osis in animal cells. S ill, he e a e caspase-like p o eases in ol ed in plan PCD [5]. Analyses ca ied ou in di e en plan sys ems ha e iden i ied se e al ypes o p o eases in ol ed in cell dea h, which include me acaspases [6], sub ilisin-like p o eases [7], and acuola p ocessing enzymes [8]. The e o e, bo h mo phological and biochemical cha ac e is ics sugges ha plan s and animals ha e de eloped di e en s a egies ha pe o m cell dea h. The s udy o PCD has been a majo ield o esea ch in di e en animal model sys ems no only because i is an essen ial p ocess o unde s and de elopmen , bu also because de egula ion o PCD causes al e a ions o he cellula homeos asis, which ha e impo an implica ions associa ed wi h diseases, including cance o neu odegene a i e p ocesses [9]. A he mo phological le el, animal PCD akes place by wo well- es ablished mechanisms, apop osis and nec osis [10]. Apop osis is cha ac e ized by ac i e plasma memb ane blebbing and cell agmen a ion, o ming he so-called 5 apop o ic bodies, which a e e en ually engul ed by phagocy es. In pa allel, he nucleus unde goes d ama ic modi ica ions, which include diso ganiza ion o he nuclea en elope, ch oma in condensa ion and in e nucleosomal deg ada ion o DNA in agmen s o 180-200 bp and mul ime s o i , o ming a cha ac e is ic ladde , which cons i u es a hallma k o apop osis [11]. In con as , nec osis is cha ac e ised by he up u e o he plasma memb ane and he consequen deg ada ion o in acellula con en s. Nec osis lacks he mo phological ea u es o apop osis, no ably he o ma ion o apop o ic bodies. Inc easing a en ion has been de o ed o au ophagy, a p ocess o cell sel -diges ion in which cellula componen s a e engul ed in esicles, called au ophagosomes, p io o hei deg ada ion by lysosomes. I is well-es ablished ha au ophagy has p o-dea h unc ions, bu his p ocess may also ha e p o-su i al unc ions, and he ela ionship o au ophagy wi h apop osis is s ill he subjec o in ense deba e [12]. The nucleus is he majo a ge o he cell deg ada ion machine y a he onse o PCD. In apop o ic animal cells, he nucleus unde goes a massi e eo ganiza ion, which includes he condensa ion o ch oma in and in e nucleosomal agmen a ion o DNA [11]. Condensa ion o ch oma in has also been desc ibed in di e en plan sys ems. This is he case o nuclei om nucella cells unde going PCD du ing whea g ain de elopmen , he ch oma in o which condenses in a mo phologically simila manne as occu s in apop o ic animal cells [13]. Simila ly, DNA ladde ing is also a hallma k o PCD in di e en plan sys ems such as pea ca pel senescence [14]. Howe e , i should be no ed ha bo h ch oma in condensa ion and DNA ladde ing a e no as consis en PCD ma ke s in plan s as hey a e in animal cells. The e o e, despi e he clea mo phological and biochemical di e ences o PCD in plan s and animals, he phase o nuclea disman ling seems o ha e simila i ies in bo h ypes o cells. Indeed, ac o s in ol ed in nuclea disman ling om plan cells a e able o induce apop o ic mo phology and DNA agmen a ion in human cells [15], which sugges s he possibili y o common mechanisms in PCD o cells om bo h kingdoms, a leas a he s age o nucleus disman ling. In his e iew, we will summa ize he cu en knowledge o he p ocess o nuclea disman ling du ing PCD in plan sys ems, discussing he simila i ies and di e ences wi h he p ocess in animal sys ems. 2. An o e iew o nuclea disman ling in animal cells 6 The con en o he nucleus, he nucleoplasm, is sepa a ed om he cy oplasm by a complex memb anous nuclea en elope o med by ou e and inne nuclea memb anes, which de ine he pe inuclea space. The nuclea en elope is pene a ed by nuclea po e complexes ha media e he nucleo-cy oplasmic in e change in bo h di ec ions [16]. The nuclea ma ix a he in e nal side o he nuclea en elope ac s as a skele on de ining nuclea size and shape. Se e al nuclea memb ane p o eins localized o he inne side o he nuclea en elope p o ide binding si es o ch oma in and nuclea ma ix in animals and plan s. In animal cells he nuclea ma ix is composed o lamins and lamin-associa ed p o eins [17], nuclei o plan cells lack his s uc u e, wi h sca old and s uc u al suppo exe ed by coiled p o eins [18]. Mo phological and biochemical analyses ha e led o conside able ad ances o ou knowledge o nuclea disman ling du ing animal apop osis [11]. The p o ein p o ile o he nucleus in cells unde going apop osis is modi ied by he appea ance o ansc ip ion ac o s, p o ein kinases, p o eases and DNases, among o he p o eins. These p o eins a e p obably ansloca ed om he cy oplasm, as schema ically shown in Figu e 1. One o he ea lies e en s aking place du ing nuclea disman ling is he p o eolysis o ma ix a achmen egion-binding p o eins, which ancho ch oma in o he sca old [19]. This limi ed clea age may open nuclease si es on he ch oma in s uc u e allowing agmen a ion o DNA, which acili a es he subsequen p o eolysis o he bulk o nuclea ma ix p o eins (Figu e 1). Se e al memb ane p o eins localized o he inne side o he nuclea en elope, such as lamin B ecep o , lamin-associa ed polypep ide 2α and nucleopo in Nup 153, a e connec ed o ch oma in. The clea age o hese p o eins p omo es he de achmen o ch oma in om he nuclea en elope, which esul s in nuclea po e clus e ing. Finally, i has been specula ed ha clea age o componen s o he nuclea po e complex and he nuclea anspo machine y may s imula e an inc ease in nuclea po e pe meabili y, acili a ing p o ein ansloca ion om he cy oplasm in o he nucleus [19]. Pos - ansla ional modi ica ions o nuclea p o eins seem o ha e an impo an unc ion in nuclea disman ling du ing apop osis. His ones H2, H3 and H4, lamins and HMGA1a p o ein a e hype phospho yla ed, whe eas his one H1 is dephospho yla ed jus be o e DNA agmen a ion [19]. I is wo h compa ing nuclea en elope disassembly du ing mi osis and apop osis because diso ganiza ion o his s uc u e may sha e common mechanisms in bo h p ocesses. Nup98, a pe iphe al nucleopo in 7 localized on bo h sides o he nuclea en elope, con ains 13 phospho yla ion si es ha a e successi ely phospho yla ed by mi o ic kinases, d i ing nuclea po e complex disassembly and nuclea en elope pe meabiliza ion du ing mi osis [20]. Hype - phospho yla ion o Nup98 and o he nucleopo ins also seems o ha e a key egula o y ole in apop osis. The pos - ansla ional modi ica ions o nuclea p o eins a e p esumably impo an o h ee e en s: ch oma in condensa ion, accessibili y o nucleases o DNA and he b eakdown o he lamina. 3. Simila i ies in nuclea disman ling in animal and plan cells unde going PCD As men ioned abo e, animal cell nuclei unde go e y cha ac e is ic mo phological changes du ing apop osis. The nucleus becomes agmen ed and he agmen s mo e o apop o ic bodies, which a e subsequen ly phagocy osed by mac ophages, pa enchymal o neoplas ic cells and deg aded by phagolysosomes [21]. The e o e, he nucleus o apop o ic animal cells becomes deg aded inside ano he cell. In con as , in plan cells unde going PCD, he nucleus is no deg aded in ano he cell, which is a clea di e ence o nuclea disman ling be ween plan and animal cell dea h. Despi e hese di e ences, nuclea ex ac s o e opoxide-induced apop o ic human cells igge ed apop o ic mo phology o plan cell nuclei [15]. In he same way nuclea ex ac s om whea nucella cells unde going PCD induce apop o ic mo phology and DNA agmen a ion in nuclei om human cells (Figu e 2). These esul s sugges he exis ence o common mechanisms in he machine y o nuclea disman ling in animal and plan cells. CAD (Caspase Ac i a ed DNase) is he i s nuclease in apop o ic animal cells esponsible o he cha ac e is ic in e nucleosomal deg ada ion o DNA [22]. CAD is main ained in an inac i e s a us by he o ma ion o a complex wi h i s inhibi o [23]. The clea age o he inhibi o in apop o ic cells eleases ac i e CAD, hus allowing he subsequen deg ada ion o DNA [24]. The inding ha nuclea ex ac s om plan cells unde going PCD can igge apop o ic mo phology and DNA agmen a ion in nuclei om human cells p omp ed us o sea ch o common elemen s o nuclea disman ling in animal and plan cells. No candida e genes ha e been iden i ied so a encoding pu a i e CAD o i s inhibi o in plan s. Apop osis-inducing ac o s ex ac ed om nuclei o plan cells unde going PCD we e no inhibi ed by mammalian CAD inhibi o s (Figu e 2B). Zn2+ and EDTA, inhibi o s o PCD- ela ed Ca2+ and/o Mg2+-dependen endonucleases 8 [15], inhibi ed he induc ion o animal apop osis (Figu e 2B). These esul s sugges ha a CAD ype nuclease is no esponsible o DNA agmen a ion in plan cell nuclei unde going PCD. The e o e nuclea disman ling in plan s seems o in ol e di e en ac o s om hose in animals. Sea ch o plan homologues o he componen s o animal cell apop osis has been ca ied ou by bioin o ma ic app oaches based on sequence simila i y, which ha e no gi en posi i e esul s. The iden i ica ion o possible sha ed genes will equi e sea ches based on s uc u e and unc ion a he han sequence. 3.1. Signalling ha commi s nuclea disman ling in plan s The p ocess o PCD leading o nuclea disman ling can be schema ically subdi ided in o h ee majo phases: signalling, execu ion and nuclea disman ling i sel . The signalling and execu ion phases o PCD a e beyond he scope o his e iew. S ill, some ecen ad ances in model plan sys ems, which sugges unc ional conse a ion o key e en s egula ing PCD, a e he e discussed. The ice ansc ip ion ac o OsNAC4 is ansloca ed in o he nucleus in a phospho yla ion-dependen manne in pa hogen- igge ed hype sensi i e esponses. I ac i a es a Ca2+-dependen nuclease, which p omo es nuclea DNA agmen a ion [25]. The me acaspase mcII-Pa is ansloca ed om he cy oplasm o he nucleus du ing No way sp uce (Picea abies) emb yogenesis and acili a es cell dea h by clea ing a phylogene ically conse ed nuclease [26, 27]. A mi ogen-ac i a ed p o ein kinase appea s as a signalling ac o du ing ea ly PCD in Papa e hoeas pollen, s imula ing DNA agmen a ion [28]. The pa hway o PCD culmina es in he p ocess o nuclea disman ling in bo h plan and animal cells. As discussed abo e, he nuclei o plan and animal cells ha e e y simila s uc u es and, despi e he di e ences, unde go simila modi ica ions, he mos ele an being ch oma in condensa ion and DNA agmen a ion, in dying cells. Thus he ques ion a ises whe he he key e en s o nuclea disman ling a e simila in bo h ypes o cells. The mos ele an e en s aking place du ing nuclea disman ling in animal and plan PCD a e summa ized in Table 1. The i s e en is he ansloca ion o di e en ac o s and enzymes o he nucleus ha ini ia e he p ocess. In apop o ic animal cells he mos ele an p ocess ha akes place a his s age is he ansloca ion o he CAD complex wi h i s inhibi o [23, 24]. The ele an e en in plan s a his s age is he ansloca ion o ansc ip ion ac o s, such as OsNAC4 [25], and he me acaspase mcII- 9 Pa [26]. Then, he ma u a ion o apop ogenic ac o s, o inac i a ion o hei inhibi o s, occu s. The ele an ac i i y illus a ing his s age is he clea age o he inhibi o o CAD by caspase-3 in animal cells unde going apop osis [24], and he clea age o he Tudo S aphylococcal Nuclease (TSN) by me acaspase mcII-Pa [27] in plan PCD. The dis up ion o he nucleo-cy oplasmic ba ie , acili a ed by limi ed diges ion o some nucleopo ins o he nuclea po e complex, which al e s he pe meabili y h ough he po e o an exclusion size o ca. 30 kDa o mo e han 70 kDa, has been documen ed in apop o ic animal cells [29] bu , o ou knowledge, no in plan cells unde going PCD. Simila ly, he p o ec ion om clea age o o he nucleopo ins un il he end o he dea h p ocess has been documen ed only in apop o ic animal cells [30], bu no in plan cells. A se ies o e en s ollows wi h he clea age o DNA in o di e en con o ma ions (ch oma in loop DNA, oligonucleosomal DNA o naked DNA) ca alysed by di e en nucleases. Examples o hese nucleases ha e been epo ed bo h in animal and plan PCD (Table 1). Finally, nuclea po e complex clus e ing, which may acili a e nuclea agmen a ion and ch oma in elease o he cy oplasm, as well as engul men o nuclea agmen s, ha e also been epo ed in bo h ypes o cells [13, 19, 32, 36]. 3.2. Sequence o e en s o plan nuclea disman ling du ing PCD Two ypes o e en s can be dis inguished in he p ocess o nuclea disman ling; hose a ec ing ch oma in s uc u e and DNA agmen a ion, and hose a ec ing he nuclea en elope. The mos cha ac e is ic s uc u al ea u e in cells unde going PCD is ha ch oma in becomes inc easingly condensed. This p ocess begins a he inne side o he nuclea en elope, whe e disc e e pa ches o condensed ch oma in can be obse ed. In animal cell apop osis he p og ession o ch oma in condensa ion can be classi ied in h ee s ages: s age I, o ing condensa ion, s age II, o necklace condensa ion, and s age III, o nuclea collapse/disassembly [37, 38], as schema ized in Figu e 3A. These s ages a e less clea ly de ined in plan cells, bu he p ocess o ch oma in condensa ion p og esses essen ially in he same way and culmina es in he o ma ion o disc e e domains o condensed ch oma in [15, 26]. Two ypes o ch oma in condensa ion mo phologies appea du ing pe al senescence: a) agmen s o condensed ch oma in inside he nucleus and b) a la ge numbe o DNA sphe ical bodies, each en eloped by a 16 [26] P.V. Bozhko , e al., Cys eine p o ease mcII-Pa execu es p og ammed cell dea h du ing plan emb yogenesis. P oc. Na l. Acad. Sci. USA 102 (2005) 14463-14468. [27] J.F. Sund öm, e al., Tudo s aphylococcal nuclease is an e olu iona ily conse ed componen o he p og ammed cell dea h deg adome. Na . Cell Biol. 11 (2009) 1347-1354. [28] S. Li, Y. Samaj, V.E. F anklin-Tong, A Mi ogen-Ac i a ed P o ein Kinase signals o p og ammed cell dea h induced by sel -incompa ibili y in Papa e pollen. Plan Physiol. 145 (2007) 235-245. [29] A. K ame , e al., Apop osis leads o a deg ada ion o i al componen s o ac i e nuclea anspo and a dissocia ion o he nuclea lamina. P oc. Na l. Acad. Sci. USA 105 (2008) 11236-11241. [30] M. Pa e, e al., Caspases a ge only wo a chi ec u al componen s wi hin he co e s uc u e o he nuclea po e complex. J. Biol. Chem. 281 (2006) 1296-1304. [31] F. Obe hamme e al., Apop o ic dea h in epi helial cells: clea age o DNA o 300 and/o 50 kb agmen s p io o o in he absence o in e nucleosomal agmen a ion. EMBO J. 12 (1993) 3679-3684. [32] L.H. Filono a, e al.Two wa es o p og ammed cell dea h occu du ing o ma ion and de elopmen o soma ic emb yos in he gymnospe m, No way sp uce. J. Cell Sci. 113 (2000) 4399-4411. [33] J.C. S ein, G. Hansen, Mannose induces an endonuclease esponsible o DNA ladde ing in plan cells. Plan Physiol. 121 (1999) 71-79. [34] F. Domínguez, J. Mo eno, F.J. Cejudo, A gibbe ellin-induced nuclease is localized in he nucleus o whea aleu one cells unde going p og ammed cell dea h. J. Biol. Chem. 279 (2004) 11530-11536. [35] J. I o, H. Fukuda, ZEN1 is a key enzyme in he ea ly deg ada ion o nuclea DNA du ing p og ammed cell dea h o achea y elemen s. Plan Cell 14 (2002) 3201- 3211. [36] L.P. E wig, P.M. Henson, Clea ance o apop o ic cells by phagocy es. Cell Dea h Di . 15 (2008) 243-250. [37] M. Kihlma k, G. Im eh, E. Hallbe g, Sequen ial deg ada ion o p o eins om he nuclea en elope du ing apop osis. J. Cell Sci. 114 (2001) 3643-3653. [38] S. Toné, e al., Th ee dis inc s ages o apop o ic nuclea condensa ion e ealed by ime-lapse imaging, biochemical and elec on mic oscopy analysis o cell- ee apop osis. Exp. Cell Res. 313 (2007) 3635-3644. [39] T. Yamada, K. Ichimu a, W.G. Van Doo n, DNA deg ada ion and nuclea degene a ion du ing p og ammed cell dea h in An i hinum, A gy an hemum and Pe unia. J. Exp. Bo . 57 (2006) 3543-3552. [40] F. Domínguez, J. Mo eno, F.J. Cejudo, The scu ellum o ge mina ed whea g ains unde goes p og ammed cell dea h: iden i ica ion o an acidic nuclease in ol ed in nucleus disman ling. J. Exp. Bo . 63 (2012) 5475-5485. [41] S. Fa age-Ba hom, e al., Localiza ion o he A abidopsis senescence- and cell dea h-associa ed BFN1 nuclease: om he ER o agmen ed nuclei. Mol. Plan 4 (2011) 1062-1073. [42] E. Fe ando-May, e al., Caspases media e nucleopo in clea age, bu no ea ly edis ibu ion o nuclea anspo ac o s and modula ion o nuclea pe meabili y in apop osis. Cell Dea h Di . 8 (2001) 495-505. [43] J. Fise o a, E. Kisele a, M.W. Goldbe g, Nuclea en elope and nuclea po e complex s uc u e and o ganiza ion in obacco BY-2 cells. Plan J. 59 (2009) 243- 255. 17 [44] K. Tamu a, Y. Fukao, M. Iwamo o, T. Ha agushi, I. Ha a-Nishimu a, Iden i ica ion and cha ac e iza ion o nuclea po e complex componen s in A abidopsis haliana. Plan Cell 22 (2010) 4084-4097. [45] J. Bo uc, X. Zhou, I. Meie , Dynamics o he plan nuclea en elope and nuclea po e. Plan Physiol. 158 (2012) 78-86. [46] P.O. Lim, H.J.Kim, H.G. Nam, Lea senescence. Annu. Re . Plan Biol. 58 (2007) 115-136. [47] V. Buchanan-Wollas on e al., Compa a i e ansc ip ome analysis e eals signi ican di e ences in gene exp ession and signalling pa hways be ween de elopmen al and da k/s a a ion-induced senescence in A abidopsis. Plan J. 42 (2005) 567-58. [48] E. B eeze, e al., High- esolu ion empo al p o iling o ansc ips du ing A abidopsis lea senescence e eals a dis inc ch onology o p ocesses and egula ion. Plan Cell 23(2011) 873-894. [49] S-D.Yang, P.J. Seo, H-K Yoog, C-M. Pa k, The A abidopsis NAC T ansc ip ion ac o VNI2 in eg a es abscisic acid signals in o lea senescence ia he COR/RD. Plan Cell 23 (2011) 2155-2168. [50] A. Wu, e al., Jungb unnen1, a eac i e oxygen species- esponsi e NAC ansc ip ion ac o , egula es longe i y in A abidopsis. Plan Cell 24 (2012) 482- 506. [51] S. Tu ne , P. Gallois, D. B own, T achea y elemen di e en ia ion. Annu. Re . Plan Biol. 58 (2007) 407-433. [52] C.L. Cou ois-Mo eau e al., A unique p og am o cell dea h in xylem ibe s o Populus s em. Plan J. 58 (2009) 260-274. [53] R. Ba elli, e al., Changes in ul as uc u e, p o ease and caspase-like ac i i ies du ing lowe senescence in Lilium longi lo um. Plan Sci. 180 (2011) 716-725. [54] B. Bollhöne , J. P es ele, H. Tuominen, Xylem cell dea h: eme ging unde s anding o egula ion and unc ion, J. Exp. Bo . 63 (2012) 1081-1094. [55] J.S. G eenwood, M. Helm, C. Gie l, Ricinosomes and endospe m ans e cell s uc u e in p og ammed cell dea h o he nucellus du ing Ricinus seed de elopmen . P oc. Na l. Acad. Sci. USA 102 (2005) 2238-2243. [56] C. Andeme-Ondzighi, D.A. Ch is ophe , E.J. Cho, S-C. Chang, A. S aehelin, A abidopsis p o ein disul ide isome ase-5 inhibi s cys eine p o eases du ing a icking o acuoles be o e p og ammed cell dea h o he endo helium in de eloping seeds. Plan Cell 20 (2008) 2205-2220. [57] I. Ha a-Nishimu a, N. Ha sugai, The ole o acuole in plan cell dea h. Cell Dea h Di . 18 (2011) 1298-1304. [58] J. Balk, S.K. Chew, C.J. Lea e , P.F. McCabe, The in e memb ane space o plan mi ochond ia con ains a DNase ac i i y ha may be in ol ed in p og ammed cell dea h. Plan J. 34 (2003) 573-583. [59] S.M. Doyle, M. Diamond, P.F. McCabe, Chlo oplas and eac i e oxygen species in ol emen in apop o ic-like p og ammed cell dea h in A abidopsis suspension cul u es. J. Exp. Bo . 61 (2010) 473-482. [60] A.P. Sme enko, P.V. Bozhko , L.H. Filono a, S. on A nold, P.J. Hussey, Re- o ganiza ion o he cy oskele on du ing de elopmen al p og ammed cell dea h in Picea abies emb yos. Plan J. 33 (2003) 813-824. [61] P. Robe s, e al., Piecemeal mic oau ophagy o nucleus in Saccha omyces ce e isiae. Mol. Biol. Cell 14 (2003) 129-141. [62] Y.E. Pa k, e al., Au ophagic deg ada ion o nuclea componen s in mammalian cells. Au ophagy 5 (2009) 795-804. 18 [63] J. Shoji, T. Kikuma, M. A ioka, K. Ki amo o, Mac oau ophagy-media ed deg ada ion o whole nuclei in he ilamen ous ungus Aspe gillus o yzae. Plos One 5 (2010) e15650. [64] D.C. Bassham, e al., Au ophagy in de elopmen and s ess esponses o plan s. Au ophagy 2 (2006) 2-11. [65] S. Saha a, e al., Acinus is a caspase-3-ac i a ed p o ein equi ed o apop o ic ch oma in condensa ion. Na u e 408 (1999) 168-173. [66] A.S. Habe man, M.A. Akba , S. Ray, H. K äme , D osophila acinus encodes a no el egula o o endocy ic and au ophagic a icking. De elopmen 137 (2010) 2157-2166. [67] E.J. Wol e ing, Dea h p o eases: ali e and kicking. T ends Plan Sci. 15 (2010) 185-188. [68] T.A. Di me , N.J. S acey, K. Sugimo o-Shi asu, E.J. Richa ds, LITTLE NUCLEI genes a ec ing nuclea mo phology in A abidopsis haliana. Plan Cell 19 (2007) 2793-2803. 19 Legends o igu es Fig. 1. Key e en s o nuclea disman ling du ing apop osis. In animal cells he p ocess o apop osis culmina es in nucleus disman ling. This p ocess equi es he ansloca ion o p o eins om he cy oplasm o he nucleus, which p obably occu s in se e al wa es. Some o he key e en s o nuclea disman ling a e he p o eolysis o nuclea ma ix and nuclea en elope p o eins, allowing he de achmen o he nuclea en elope om he ch oma in, he subsequen ch oma in condensa ion and he clus e ing o nuclea po e complex. Clea age o nuclea po e complex p o eins p o okes he dis up ion o nucleocy oplasmic ba ie , acili a ing he en ance o apop o ic ac o s. The p o eolysis o ch oma in-associa ed p o eins close o he de achmen o he nuclea en elope may open si es o nuclease hype sensi i i y p omo ing DNA agmen a ion by di e en nucleases. P o ein phospho yla ion, along wi h o he pos - ansla ional modi ica ions, is needed o acili a e nuclea ma ix dis up ion, ch oma in condensa ion and DNA agmen a ion. Finally, nuclea agmen a ion is p oduced wi h he o ma ion o apop o ic bodies and engul men by mac ophages. Fig. 2. Ch oma in condensa ion and DNA agmen a ion in human cells can be p omo ed by plan apop osis-inducing ac o s. A, HCT116 human cells we e ea ed wi h nuclea ex ac s om whea nucella cells unde going PCD. Clea pa ches o ch oma in condensa ion can be obse ed in he nucleus a e s aining wi h p opidium iodide. B, DNA ex ac ed om hese cells was analysed in aga ose gels and s ained wi h e hidium b omide. C, con ol un ea ed cells; +N, samples ea ed wi h nuclea ex ac s om whea nucella cells unde going PCD, in he absence (-) o he p esence o pu i ied Inhibi o o CAD (ICAD), Zn2+ o EDTA. This esul has no p e iously been epo ed, de ails o expe imen al condi ions as p e iously desc ibed [19]. Fig. 3. The p oposed sequence o e en s o nuclea disman ling du ing plan PCD in ol es ch oma in condensa ion, DNA agmen a ion and nuclea en elope dis up ion. A, Fea u es o ch oma in condensa ion dis inguishing ing, necklace and collapse/disassembly mo phologies [39]. B, P og essi e agmen a ion o DNA: high molecula weigh DNA clea age, low molecula weigh DNA clea age and naked DNA unspeci ic clea age. C, Nuclea en elope disassembly. Sequen ial clea age o plan nucleopo ins Nup 93, Nup 96, Nup 214, Nup 50, Nup 62 and Tp /NUA was p oposed 20 based on apop o ic animal cells [30]. P o eolysis o plan lamin-like p o eins and Nup 136 nucleopo in was p oposed based on he simila ole o animal lamins and Nup 155, al hough he e is no sequence homology. 21 Table 1 Rele an e en s in nuclea disman ling E en Examples and Re e ences Animals Plan s T ansloca ion o he nucleus CAD-Inhibi o complex [11, 23, 24] T ansc ip ion ac o OsNAC4 [25] Me acaspase mcII-Pa [26] P ocessing o apop ogenics ac o s o clea age o hei inhibi o s Clea age o CAD inhibi o by caspase-3 [24] Clea age o udo s aphylococcal nuclease (TSN) by a me acaspase mcII-Pa [27] Dis up ion o nucleocy oplasmic ba ie Deg ada ion o cy oplasmic ilamen s and nuclea baske om nuclea po e complex [29] n.d. P o ec ion o clea age si es o some nucleopo ins Nucleopo in Nup62 [30] n.d. Accessibili y o he con o ma ion o DNA - Ch oma in loops Ch oma in loop nuclease [31] Ch oma in loop nuclease [32] - In e nucleosomal DNA CAD nuclease [22, 23] D-mannose-induced nuclease [33] PCD- ela ed nuclease [15, 34] - Naked DNA Di e en nucleases [11] ZEN1 nuclease [35] Nuclea Po e Complex clus e ing Nuclea Po e Complex clus e ing in apop osis [19] Nuclea Po e Complex clus e ing in plan PCD [32] Nuclea agmen engul men Phagocy osis o apop o ic bodies by mac ophages [36] Au ophagic p ocess o emo e nuclea agmen s [13, 32] n.d.: no de e mined 22 Table 2 Sequence o cy oplasmic e en s p epa ing o plan nuclea disman ling O ganelle E en Re e ences ER-de i ed compa men s Accumula ion and elease o cys eine p o eases and nucleases in he onse o PCD [41, 55] ER-Golgi Chape oning and inhibi ion o cys eine p o eases by p o ein disul ide isome ase-5 du ing a icking o acuole be o e PCD [56] Vacuole (PSV and Ly ic Vacuole) -Sel -p ocessing o acuola p ocessing enzyme a acid pH -Ma u a ion o p ecu so s o PR p o eins and hyd olases by acuola p ocessing enzyme -Accumula ion o aspa a e p o eases, cys eine p o eases and nucleases un il hei elease in PCD -Tonoplas dis up ion [4, 57] Mi ochond ia Release o endonucleases, cy och ome c and o he apop ogenic ac o s [58] Cho oplas Release o ROS [59] Cy oskele on Depolyme iza ion o mic o ubule and eo ganiza ion o ac in ne wo k p o iding a skele on o igge au ophagosome o ma ion and p omo ing au ophagic mo emen s o cell con en engul men [60] Au ophagosomes and au ophagic acuoles Diges ion o emnan s o memb ane-less nuclea agmen s [13, 32, 40] 23 Ea ly p o eolysis o MAR-binding p o eins De achmen o he nuclea en elope om ch oma in B eakdown o nuclea ma ix and en i e nucleus P o eases T ansc ip ion Fac o s P o ein kinases DNases Inc ease/Modi ica ion in nuclea po e pe meabili y TRANSLOCATION Nuclea Po e Complex clus e ing P o eases T ansc ip ion Fac o s P o ein kinases Dnases P o eolysis o nuclea memb ane and po e p o eins Ch oma in condensa ion Opened si es o nuclease hype sensi i i y DNA F agmen a ion P P P CYTOPLASM NUCLEUS Nuclea En elope Nuclea Ma ix Nuclea Po e Complex P o eoly ic e en PPhospho yla ionCh oma in Figu e 1 24 2.0 1.0 0.6 0.4 0.2 kbp C +N -ICAD Zn EDTA 8.00 μm A B Figu e 2 25 Nuclea baske ONM INM Nuclea Ma ix Cy oplasmic ilamen s Nup 93 Nup 96 Nup 62? Nup 214 Nup 50 Lamin-like p o eins Tp /NUA Nup 136 S age I Necklace condensa ion Ring pe iphe al condensa ion Collapse condensa ion S age II S age III 50 kpb Loop DNases 30 nm DNA ilamen “Beads on a s ing” DNA ilamen In e nucleosomal DNases Caspase-like p o eases O he p o eases 180 bp oligome s DNA ilamen s DNA smea “Naked” DNA ilamen s Unspeci ic DNases 50 kbp oligome s DNA ilamen A Ch oma in Condensa ion B DNA F agmen a ion C Nuclea En elope / Nuclea Po e Disassembly Figu e 3