He edi as 136: 219–226 (2002)
Gene ic basis o ichome p oduc ion in A abidopsis ly a a
KATRI KA
8
RKKA
8
INEN
1
and JON A
,
GREN
2
1
Depa men o Biological and En6i onmen al Science,Uni6e si y o Jy6a¨skyla¨,Jy6a¨skyla¨,Finland
2
Depa men o Plan Ecology,E6olu iona y Biology Cen e,Uppsala Uni6e si y,Uppsala,Sweden
Ka¨ kka¨inen, K. and A
,
g en, J. 2002. Gene ic basis o ichome p oduc ion in A abidopsis ly a a.—He edi as
136
: 219–226.
Lund, Sweden. ISSN 0018-0661. Recei ed No embe 2, 2001. Accep ed May 29, 2002
Lea ichomes may p o ec plan s agains he bi o ous insec s, and may inc ease ole ance o d ough and UV- adia ion.
The pe ennial he b A abidopsis ly a a (B assicaceae) is polymo phic o ichome p oduc ion and occu s in a glab ous and
ichome-p oducing o m. In addi ion, he e is quan i a i e a ia ion in ichome densi y among ichome-p oducing
plan s. To examine he gene ic basis o glab ousness, we conduc ed con olled c osses wi h plan s o igina ing om wo
na u al popula ions in Sweden (one polymo phic o ichome-p oduc ion, and one consis ing o glab ous plan s only). In
addi ion, we es ima ed he he i abili y o ichome numbe om pa en -o sp ing eg essions o plan s o igina ing om
he polymo phic popula ion. C osses be ween glab ous plan s esul ed in glab ous o sp ing only, whe eas c osses be ween
glab ous and ichome-p oducing plan s, and c osses be ween ichome-p oducing indi iduals, esul ed in ei he all
ichome-p oducing o sp ing o bo h pheno ypes. In seg ega ing c osses be ween ichome-p oducing plan s, he a io o
glab ous: ichome-p oducing o sp ing did no de ia e signi ican ly om 1:3, while in seg ega ing c osses be ween
glab ous and ichome-p oducing indi iduals he a io did in mos cases no de ia e om 1:1. Wi hin- and be ween-pop-
ula ion c osses ga e simila esul s. The he i abili y o ichome numbe es ima ed om eg ession o o sp ing on
mid-pa en was high (h
2
9SE, 0.6590.15). The esul s sugges ha glab ousness is inhe i ed in a simple Mendelian
ashion, wi h he allele coding o ichome p oduc ion being dominan o e ha o glab ousness. They u he indica e
ha glab ousness is due o a mu a ion a he same locus in bo h popula ions.
Ka i Ka¨ kka¨inen,Finnish Fo es Ins i u e,Van aa Resea ch Cen e,P.O.Box
18
,
01301
Van aa Finland. E-mail:
[email p o ec ed]
The gene ic basis o adap i e ai s de e mines how
hey can be moulded by selec ion, bu is s ill poo ly
known. Many adap i e cha ac e s a y con inuously
and ha e wi hin a quan i a i e-gene ic amewo k
been assumed o be in luenced by a la ge numbe o
genes, each wi h a small e ec . Howe e , ecen
s udies ha e sugges ed ha adap i e ai s can be
con olled by ew genes wi h la ge e ec s (S
CHEMSKE
and B
RADSHAW
1999; J
OHANSON
e al. 2000; F
RARY
e al. 2000; W
EBER
e al. 1999). On he o he hand,
some ai s ha ha e been hough o ha e a simple
monogenic inhe i ance ha e been ound o be much
mo e complex han ea lie was belie ed (S
CRIVER
and W
ATERS
1999). Addi ional s udies o he gene ic
basis o adap i e cha ac e s a e he e o e clea ly
needed.
T ichomes a e uni- o mul icellula hai s ha de-
elop on he lea es, sepals, and s ems o plan s, and
may se e se e al unc ions. They may p o ec plan s
agains UV- adia ion and d ough (E
HLERINGER
1984; S
KALTSA
e al. 1994; E
SPIGARES
and P
ECO
1995), and also agains damage caused by he bi o es
(L
EVIN
1973; A
,
GREN
and S
CHEMSKE
1993; V
ALVERE
e al. 2001) and pa hogens (H
AGLEY
e al. 1980). The
p oduc ion o ichomes may hus be bene icial o
se e al easons, bu can also be associa ed wi h a
cos : In en i onmen s whe e ichomes do no con e
an ad an age, glab ous plan s may be able o alloca e
mo e esou ces o g ow h and ep oduc ion (A
,
GREN
and S
CHEMSKE
1993; B
ERGELSON
1994; M
AURICIO
and R
AUSHER
1997; M
AURICIO
1998).
Gene ic a ia ion in lea ichome numbe has been
de ec ed in se e al membe s o he B assicaceae, in-
cluding A abidopsis haliana (M
AURICIO
and
R
AUSHER
1997), B assica apa (A
,
GREN
and
S
CHEMSKE
1994), and Sinapis a 6ensis (R
OY
e al.
1999). Mu a ions a ec ing ichome o ma ion ha e
been iden i ied in A. haliana and many o hem ha e
also been cloned and sequenced (M
ARKS
1997). T i-
chome densi y may u he be in luenced by en i on-
men al condi ions (A
GRAWAL
1999; R
OY
e al. 1999).
The ou c ossing pe ennial he b A abidopsis ly a a
is polymo phic o ichome p oduc ion and occu s in
a glab ous (G) and a ichome-p oducing o m (T).
In addi ion, he e is conside able a ia ion in i-
chome densi y among ichome p oducing A.ly a a.
To in es iga e he inhe i ance o glab ousness and
whe he he gene ic basis o glab ousness in A.ly a a
is consis en ac oss popula ions in Sweden, we con-
duc ed c osses be ween glab ous and ichome-p o-
ducing plan s o igina ing om wo na u al
popula ions sepa a ed by abou 32 km (one polymo -
phic o ichome-p oduc ion, and one consis ing o
glab ous plan s only). We documen ed he seg ega-
ion o glab ousness in he esul ing o sp ing. We
u he es ima ed he he i abili y o ichome numbe
K.Ka¨ kka¨inen and J.A
,
g en220 He edi as 136 (2002)
om pa en -o sp ing eg essions o plan s o igina -
ing om he polymo phic popula ion.
MATERIAL AND METHODS
The species
A abidopsis ly a a (L.) O’Kane and Al-Shehbaz ssp.
pe aea (B assicaceae, syn. A abis pe aea L., and
Ca daminopsis pe aea (L.) Hii .) is a pe ennial, sel -
incompa ible he b, closely ela ed o A. haliana L.
(P
RICE
e al. 1994; K
OCH
e al. 1999; S
AVOLAINEN
e
al. 2000). Fou geog aphically sepa a ed subspecies
ha e been iden i ied in A.ly a a:A.ly a a ssp. pe-
aea in Eu ope, A.ly a a ssp. ly a a in No h Ame -
ica, and A.ly a a ssp. kamcha ica and ssp.
kawasakiana in eas e n Asia (O’K
ANE
and A
L
-S
HEH-
BAZ
1997).
A abidopsis ly a a has a disjunc dis ibu ion in
Eu ope. I is a common species in Iceland and in he
Fa oes, and is ound in he no h-wes e n pa s o he
B i ish Isles, in sou he n Ge many and in he Alps
(J
ALAS
and S
UOMINEN
1994). In Scandina ia, A.
ly a a occu s only in wes e n No way and in a limi ed
a ea along he coas o eas e n Sweden (H
ULT
e´
N
1971).
The 5–20 cm long in lo escence is p oduced om a
lea ose e. The ose e lea es a e ypically 3–10 cm
long and 0.5–1.0 cm wide. A abidopsis ly a a may
p oduce ichomes on lea es and s ems. Lea i-
chomes o m up o i e b anches, whe eas hose on
he s ems a e p edominan ly unb anched. Among
ichome-p oducing plan s, he e is conside able a i-
a ion in he densi y o lea ichomes, om plan s
p oducing only a ew ichomes on he lea ma gin o
hose wi h lea es densely co e ed by ichomes (J
ON-
SELL
e al. 1995).
Gene ic basis o glab ousness
To examine he gene ic basis o glab ousness, we
conduc ed con olled c osses using plan s p oduced
om seeds collec ed in wo A.ly a a popula ions in
eas e n Sweden. One popula ion was polymo phic o
ichome p oduc ion and loca ed a S o s ensudden
(63°12%N, 18°48%E; p opo ion o glab ous plan s
abou 30 %), while he o he popula ion consis ed o
glab ous plan s only and was loca ed a No -
a¨lls iken (62°35%N, 18°32%E; p opo ion o
glab ous plan s 98 %). Seeds we e collec ed om
glab ous (G) and ichome-p oducing (T) plan s and
sown in a g eenhouse in he au umn 1997. The ol-
lowing sp ing, he pheno ype o lowe ing indi iduals
was sco ed as glab ous (no ichomes obse ed) o
ichome-p oducing. Plan s we e andomly assigned
as ma e nal and pa e nal pa en s o he c osses. We
c ossed he wo mo phs in all combina ions (G×G,
G×T, T×G, and T×T), and conduc ed c osses
bo h wi hin and be ween he wo popula ions. The
c osses we e epea ed wi h di e en ma e nal and
pa e nal plan s.
The seg ega ion o glab ousness was examined
among he o sp ing om 43 c osses (38 wi hin-popu-
la ion c osses and 5 be ween-popula ion c osses).
Seeds we e sown in a g eenhouse in ea ly sp ing 2000
and he pheno ypes o he seedlings (al oge he 822
indi iduals) we e sco ed h ee mon hs a e sowing.
Twen y o se en y indi iduals we e sco ed om each
o 18 c osses, while 8–10 indi iduals we e sco ed
om each o he emaining 24 c osses. C osses we e
classi ied as seg ega ing when he o sp ing included
bo h glab ous and ichome-p oducing plan s, and
non-seg ega ing when all o sp ing we e o he same
pheno ype in e ms o ichome p oduc ion.
Based on he esul s o he c osses (see below), we
pos ula ed a simple Mendelian model o he inhe i-
ance o glab ousness (a one gene, wo-allele model in
which he allele coding o ichome-p oduc ion is
dominan o e he allele coding o glab ousness).
The i o he model was e alua ed by es ing he
ollowing p edic ions: Fi s , i he glab ous pheno-
ype (G) is a ecessi e homozygo e, c osses be ween
glab ous indi iduals (G×G) should p oduce only
glab ous o sp ing. Second, c osses be ween i-
chome-p oducing indi iduals (T×T) should p oduce
ei he only ichome-p oducing o sp ing i a leas
one pa en is homozygous o ichome-p oduc ion
o , i bo h pa en s a e he e ozygous wi h espec o
he gene coding o ichome p oduc ion, p ogenies
wi h a 1:3 a io o glab ous o ichome-p oducing
indi iduals. Thi d, he o sp ing om c osses be ween
glab ous and ichome-p oducing indi iduals should
seg ega e in a 1:1 a io o glab ous o ichome-p o-
ducing plan s i he ichome-p oducing pa en is a
he e ozygo e, and all o sp ing should be ichome-
p oducing i he ichome-p oducing pa en is ho-
mozygous o he dominan allele. Finally, i
seg ega ion a ios do no di e be ween ecip ocal
c osses (G×T sT×G), ichome p oduc ion is
likely o be go e ned by nuclea genes a he han by
cy oplasmic ac o s. C osses be ween popula ions
(G×G and G×T) we e conduc ed o assess whe he
he gene ic basis o glab ousness was simila in he
popula ions.
Fo seg ega ing c osses, de ia ions om expec ed
a ios o glab ous o ichome-p oducing plan s we e
examined wi h G- es s. This was done sepa a ely o
each c oss wi h a la ge numbe o o sp ing (N=20–
70), and o da a pooled o e each c oss ype (T×T,
G×T, T×G). Fo c osses wi h la ge numbe s o
o sp ing, he da a on pheno ypes o ma e nal and
pa e nal g andmo he s (de e mined in he ield when
Gene ic basis o ichome p oduc ion in A abidopsis 221He edi as 136 (2002)
Table 1. Summa y o he esul s o
42
con olled c osses be ween glab ous
(
G
)
and ichome-p oducing
(
T
)
A abidopsis ly a a ssp.pe aea.The plan s used in he c osses o igina ed om wo na u al popula ions in eas e n
Sweden
(
No a¨lls6iken
(
N
)
and S o s ensudden
(
SU
))
.In seg ega ing c osses,bo h glab ous and ichome-p oduc-
ing plan s we e obse 6ed among he o sp ing
O sp ing pheno ypeO igin o Numbe o c ossesType o c oss To al numbe
à×ßo o sp ingin non-seg ega ingpa en al plan s
Seg ega ing Non-seg ega ingà×ßc osses
N×NG×G09
1)
G 208
03 GSU×SU 32
N×SU 0 1
2)
G42
48
3)
T 250T×TSU×SU
52 TSU×SU 81G×T
N×SU 3 0 93
T×GSU×SU 6 1 T 62
10SU×N 34
1)
One o he 208 o sp ing s udied had p oduced wo ichomes.
2)
One o he 42 o sp ing had wo ichomes
3)
In one c oss, one ou o 60 o sp ing was glab ous.
sampling seeds) we e used o in e he geno ypes o
he pa en al plan s used in he c oss.
Pheno ypic and gene ic 6a ia ion in ichome numbe
To documen he equency dis ibu ion o ichome
numbe pe lea , we g ew in he g eenhouse wo
plan s om each o 50 ma e nal amilies collec ed in
he polymo phic S o s ensudden popula ion. Th ee
mon hs a e plan ing, we coun ed he numbe o
ichomes on he adaxial (uppe ) su ace o one an-
domly selec ed lea om each plan unde a dissec -
ing mic oscope. The leng h and wid h o he sampled
lea we e measu ed o he nea es mm, and lea a ea
was es ima ed as he p oduc o hese wo measu es.
The he i abili y o ichome numbe in he
S o s ensudden popula ion was es ima ed based on
pa en -o sp ing eg essions. T ichome numbe pe
lea was de e mined as abo e o bo h pa en s and
o sp ing in he 28 con olled c osses ha esul ed in
a leas some ichome-p oducing plan s (Table 1 and
2). The mean numbe o ichomes on he uppe lea
su ace in he o sp ing was eg essed on (a) he
ma e nal pa en , (b) he pa e nal pa en , and (c) he
mid-pa en alue (F
ALCONER
and M
ACKAY
1996).
To achie e no mali y, ichome numbe pe lea was
log- ans o med (log( ichome numbe +1)) p io o
analyses.
RESULTS
Gene ic basis o glab ousness
:
con olled c osses
All c osses be ween glab ous indi iduals (wi hin and
be ween popula ions) p oduced glab ous o sp ing
only (Table 1). Fou c osses be ween ichome-p o-
ducing plan s p oduced bo h glab ous and ichome-
p oducing o sp ing, while eigh such c osses
p oduced ichome-p oducing o sp ing only (Table
1). C osses be ween he wo mo phs p oduced ei he
only ichome-p oducing indi iduals, o p ogenies
wi h bo h glab ous and ichome-p oducing plan s
(Table 1).
In seg ega ing c osses be ween ichome-p oducing
plan s, he obse ed a io o glab ous s. ichome-
p oducing o sp ing did no s a is ically de ia e om
he expec ed 1:3 a io in C oss 1 (N=62), o in he
da a pooled om ou c osses (N=86; Table 2). The
mo he s o bo h plan s used in C oss 1 we e glab ous,
hus he la e we e in e ed o be he e ozygous a he
locus causing glab ousness (Table 2).
Bo h wi hin- (SU×SU) and be ween-popula ion
c osses (N×SU o SU×N) be ween glab ous and
ichome-p oducing indi iduals esul ed in seg ega -
ing p ogenies. The a io o glab ous o ichome-p o-
ducing plan s did no de ia e om he expec ed 1:1
a io in he wo T×G c osses wi h la ge numbe o
o sp ing (one wi hin-popula ion and one be ween-
popula ion c oss), o in he pooled analysis o six
seg ega ing T×G c osses (40 glab ous s 48 i-
chome-p oducing indi iduals, G=0.73, NS). How-
e e , wo o ou seg ega ing G×T c osses p oduced
G:T a ios ha de ia ed signi ican ly om he ex-
pec ed 1:1 a io (bo h we e be ween-popula ion
c osses; Table 2). The numbe o glab ous indi iduals
was lowe han expec ed among he o sp ing o
G×T C oss 1, and highe han expec ed among he
o sp ing o G×T C oss 2. In he o he wo seg e-
ga ing G×T c osses analysed sepa a ely (one wi hin-
and one be ween-popula ion c oss), and in he pooled
analysis o G×T c osses, he a io o glab ous o
ichome-p oducing plan s did no de ia e om he
K.Ka¨ kka¨inen and J.A
,
g en222 He edi as 136 (2002)
Table 2. Compa ison o obse 6ed and expec ed a ios o glab ous
(
G
)
o ichome-p oducing o sp ing
(
T
)
in
seg ega ing c osses wi h N
20
,and in da a pooled o seg ega ing c osses o each ype.The plan s used in he
c osses o igina ed om wo popula ions o A abidopsis ly a a ssp.pe aea in eas e n Sweden
(
No a¨lls6iken
(
N
)
and S o s ensudden
(
SU
))
.The i o obse 6ed a ios o hose expec ed unde a single-locus wo-allele model wi h
he allele coding o ichome p oduc ion being dominan o6e he allele coding o glab ousness was examined wi h
G- es s
(
d =
1)
.Fo c osses ep esen ed by
20
o mo e o sp ing, he pheno ypes o he ma e nal and pa e nal
g andmo he s,and he in e ed geno ypes o pa en al plan s a e gi6en
O igin G- es O sp ing Expec ed Pheno ypes o Geno ypes o C oss ype
pheno ypes a io o à×ßà×ßpa en al plan s
1)
g andmo he s
G:T in he
GT ào sp ing ßà×ß
T×T:
22 40 1:3 3.34 NSSU×SU G G T× TC oss 1
29 57 1:3 3.25 NSPooled da a, 4 c osses
G×T:
8 22 1:1 6.68 **N×SU GC oss 1 G × T
N×SUC oss 2 31 10 1:1 11.15 *** G T ×T o × T
715C oss 3 1:1 2.91 NS G T ×T o × TN×SU
21 25 1:1 0.34 NSSU×SU GC oss 4 T ×T o × T
86 88 1:1 0.02 NSPooled da a, 8 c osses
T×G:
15 19 1:1 0.46 NSSU×NGC oss 1 G T×
SU×SUC oss 2 9 11 1:1 0.20 NS G G T×
48 1:1 0.73 NSPooled da a, 6 c osses 40
1
The allele ecei ed om he ma e nal plan is p esen ed be o e he allele ecei ed om he pa e nal plan .
expec ed 1:1 a io (eigh c osses, 86 glab ous s 88
ichome-p oducing indi iduals, G=0.02, NS; Table
2). Unde he pos ula ed model o inhe i ance o
glab ousness, he ichome-p oducing pa en in seg e-
ga ing c osses should be he e ozygous a he locus
causing glab ousness. The obse a ion ha he i-
chome-p oducing pa en had a glab ous mo he in
h ee o he seg ega ing c osses is consis en wi h his
iew (Table 2: G×T C oss 1; T×G C oss 1 and
T×G C oss 2).
Pheno ypic and gene ic 6a ia ion in ichome numbe
The plan s es ablished om seeds collec ed in he
S o s ensudden popula ion and g own in he g een-
house exhibi ed conside able a ia ion in ichome
numbe pe lea (mean=18.9, SD=32.5, N=96;
Fig. 1). The dis ibu ion o ichome numbe de ia ed
signi ican ly om he no mal dis ibu ion (Kol-
mogo o -Smi no es o no mali y 0.302, d =96;
pB0.001), wi h high alues o skewness (2.10, SE=
0.25) and ku osis (3.42, SE=0.49). This was ue
also i glab ous indi iduals we e excluded om he
analysis (Kolmogo o -Smi no 0.296, d =60, pB
0.001; skewness 1.46, SE=0.31, ku osis 0.87, SE=
0.61). Va ia ion in ichome densi y ( ichome
numbe pe uni lea a ea) was a unc ion o a ia ion
in o al numbe o ichomes p oduced, a he han
o a ia ion in lea size: ichome numbe pe uni
lea a ea was s ongly co ela ed wi h ichome num-
be pe lea ( =0.946, N=406, pB0.001), bu was
no co ela ed wi h lea a ea ( =−0.07, N=406,
NS).
The es ima es o he he i abili y o ichome num-
be pe lea ob ained om eg essions o o sp ing on
ma e nal, pa e nal and midpa en alues we e all
high (h
2
9SE, 1.1790.25, 1.0390.53, and 0.659
0.15, espec i ely, N=28, Fig. 2).
In c osses be ween glab ous and ichome-p oduc-
ing plan s mos o sp ing p oduced ewe lea i-
chomes han he ichome-p oducing pa en (Fig. 3).
Fig. 1. Pheno ypic a ia ion in ichome numbe on he
uppe side o he lea in A abidopsis ly a a ssp. pe aea.
Plan s we e aised in he g eenhouse om seeds collec ed in
he S o s ensudden popula ion, and we e sco ed o i-
chome numbe h ee mon hs a e plan ing (N=100).
Gene ic basis o ichome p oduc ion in A abidopsis 223He edi as 136 (2002)
Fig. 2. Mean numbe o lea ichomes in he o sp ing as
a unc ion o mean numbe o lea ichomes o he
pa en al plan s (mid-pa en alue) in 28 c osses conduc ed
wi h plan s o igina ing om he S o s ensudden popula-
ion. Bo h he pa en al plan s and he o sp ing we e aised
in he g eenhouse and sco ed o ichome numbe on he
uppe lea su ace h ee mon hs a e plan ing. T ichome
numbe was log- ans o med p io o analysis. The he i a-
bili y es ima e (9SE) is indica ed in he igu e.
Glab ousness may ha e a simple gene ic basis also
in o he plan species. Da a om seg ega ing c osses
indica e ha glab ousness is con olled by one, au o-
somal ecessi e gene in Silene dioica (W
ESTERBERGH
1992), and Silene la i olia (D
E
V
RIES
1900). Mo e-
o e , ichome mo phology (glandula s. non-glan-
dula ichomes) can be inhe i ed in a simple
Mendelian ashion as was ecen ly documen ed o
Da u a w igh ii (
VAN
D
AM
e al. 1999).
In o ma ion on he gene ic basis o ichome de el-
opmen sugges s ha glab ousness may ha e a simple
gene ic basis also in in A abidopsis haliana. Al hough
he e a e many genes in ol ed in ichome o ma ion,
only a ew low in he de elopmen al pa hway
(GLABROUS-1 and TTG) ha e been ound o block
ichome p oduc ion comple ely (M
ARKS
1997).
GLABROUS-1 encodes a p o ein wi h sequence
homology o a myb- ela ed ansc ip ion ac o (O
P-
PENHEIMER
e al. 1991). Plan s homozygous o he
gl1-1 allele a e i ually de oid o ichomes, al-
hough ichomes a e occasionally ound a he ma -
gin o ose e and cauline lea es. Plan s homozygous
o he weake allele gl1-2 ha e educed ichome
numbe wi h ichomes nea he ma gin o lea es
(E
SCH
e al. 1994). Mu a ion in he gene TTG1,
In con as , in c osses be ween ichome-p oducing
indi iduals, a la ge p opo ion o he o sp ing p o-
duced mo e lea ichomes han ei he pa en (Fig. 4).
DISCUSSION
Gene ic basis o glab ousness
The esul s o he p esen s udy indica e ha
glab ousness has a simple Mendelian inhe i ance in
A abidopsis ly a a ssp. pe aea, and ha glab ousness
is de e mined by allelic a ia ion a he same locus in
he wo popula ions s udied. Mo eo e , hey indica e
ha he e is conside able gene ic a ia ion in he
numbe o ichomes o med by ichome-p oducing
plan s. The ac ha c osses be ween glab ous plan s
did no p oduce any ichome-p oducing o sp ing,
while c osses be ween ichome-p oducing plan s e-
sul ed in ei he all ichome-p oducing plan s o seg-
ega ing p ogenies sugges s ha glab ousness is a
ecessi e cha ac e o ichome-p oduc ion. Mo e-
o e , he a io o glab ous: ichome-p oducing plan s
in he seg ega ing p ogenies did no s a is ically de i-
a e om he expec ed 1:3 a io. As expec ed unde a
one-locus, wo-allele model, some be ween-mo ph
c osses p oduced only ichome-p oducing o sp ing.
The a io o glab ous o ichome-p oducing plan s
did no s a is ically de ia e om he expec ed 1:1
a io in ou o he six c osses be ween glab ous and
ichome-p oducing plan s, o in he pooled analysis
o such c osses.
Fig. 3. Va ia ion in ichome numbe on he uppe lea
su ace among o sp ing om con olled c osses be ween
glab ous and ichome-p oducing plan s (G×T, C osses
1–4, and T×G C osses 1–2 in Table 2). T ichome num-
be s o ma e nal (solid line a ow) and pa e nal pa en s
(b oken line a ow) a e indica ed.

K.Ka¨ kka¨inen and J.A
,
g en224 He edi as 136 (2002)
Fig. 4. Va ia ion in ichome numbe on he uppe lea
su ace among o sp ing om con olled c osses be ween
ichome-p oducing plan s (T×T). In C oss 1, some o he
o sp ing we e glab ous, in he o he wo c osses all
p ogeny we e ichome-p oducing. T ichome numbe s o
ma e nal (solid line a ow) and pa e nal pa en s (b oken
line a ow) a e indica ed.
Russian popula ion (H
AUSER
e al. 2001) and ou
own da a on Swedish and No wegian popula ions
(Ka¨
RKK
a¨
INEN
,K
IVIM
a¨
KI
and A
,
GREN
, unpubl.) sug-
ges ha mu a ions ei he in he coding a ea o in he
egula o y egions o GLABROUS-1 may cause
glab ousness in A.ly a a.
Gene ic basis o ichome numbe
Pa en -o sp ing eg essions indica ed ha he he i a-
bili y o ichome numbe pe lea was high in he
s udied popula ion. This sugges s ha his popula ion
may espond no only o selec ion on ichome o -
ma ion pe se, bu also o selec ion on ichome
densi y. The he i abili y es ima e based on mid-pa -
en alues had a lowe s anda d e o (h
2
=0.65,
SE=0.15) han he es ima es based on ma e nal
(h
2
=1.17, SE=0.25) and pa e nal alues (h
2
=1.03,
SE=0.53). The seg ega ion o he ecessi e allele o
glab ousness may ha e con ibu ed o he high s an-
da d e o s o he wo la e es ima es. The highes
es ima e was ob ained when o sp ing ichome num-
be was eg essed on ma e nal alue, as would be
expec ed i ma e nal en i onmen al e ec s con ibu e
o a ia ion in ichome numbe (R
OACH
and W
ULFF
1987).
The skewed dis ibu ion o ichome numbe ob-
se ed in he S o s ensudden popula ion can pa ly be
a ibu ed o he occu ence o glab ous plan s. How-
e e , he dis ibu ion de ia ed om no mali y also
when he comple ely glab ous indi iduals we e ex-
cluded om he analysis. This is consis en wi h he
hypo hesis ha he e is one o se e al genes wi h
majo e ec on ichome numbe in ichome-p oduc-
ing plan s. In A abidopsis haliana, a QTL-analysis o
ichome numbe o wo eco ypes e ealed a majo
QTL (Reduced ichome numbe , RTN) ha ex-
plained 70 % o he a ia ion in ichome numbe
(L
ARKIN
e al. 1996). In a QTL-s udy on ichome
densi y o co on, one QTL wi h majo pheno ypic
e ec and a ew wi h smalle e ec s we e ound
(W
RIGHT
e al. 1999). Thus, a ew genes wi h majo
e ec may in luence a ia ion in ichome numbe in
se e al species.
C osses be ween glab ous and ichome-p oducing
plan s yielded ichome-p oducing plan s wi h a
ma kedly lowe ichome numbe han hose p o-
duced in c osses be ween ichome-p oducing plan s.
This sugges s ha he mu a ion causing glab ousness
may in luence he densi y o lea ichomes in he -
e ozygous ichome-p oducing plan s. To u he
cla i y he gene ic basis o ichome numbe in A a-
bidopsis ly a a, we a e cu en ly employing bo h com-
plex seg ega ion analysis (L
YNCH
and W
ALSH
1998),
and QTL- and candida e gene app oaches.
anspa en es a glab a1, can also esul in a com-
ple e loss o ichome o ma ion on mos a eal su -
aces (K
OORNNEEF
1981). The TTG1 gene encodes a
WD40 epea p o ein ha may egula e signal ans-
duc ion pa hways go e ning lea hai o ma ion and
an hocyanin biosyn esis (W
ALKER
e al. 1999). By
now, se e al mu a ions ha esul in he loss o show
educ ion in ichome o ma ion ha e been desc ibed
o TTG1 (W
ALKER
e al. 1999).
The glab ous pheno ype o A abidopsis ly a a may
be caused by one o he genes causing glab ousness in
A abidopsis haliana. Based on sequence a ia ion in
DNA, A.ly a a and A.halle i a e he closes known
ou c ossing ela i es o A. haliana (O’K
ANE
and
A
L
-S
HEHBAZ
1997; K
OCH
e al. 1999). Thus, genes
causing glab ousness in A. haliana a e good candi-
da es o causing glab ousness also in A.ly a a.A
ecen s udy which included a glab ous plan om a
Gene ic basis o ichome p oduc ion in A abidopsis 225He edi as 136 (2002)
ACKNOWLEDGEMENTS
This s udy was suppo ed by g an s om he Academy o
Finland and No FA o KK and om he Swedish Resea ch
Council and Fo mas o JA
,
.
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