Page 5 - Legume Genomics and Genetics

Legume Genomics and Genetics (online), 2010, Vol. 1, No.2, 7-10
http://lgg.sophiapublisher.com
TCP transcriptional factor (Wang et al., 2008). In L.
japonicus, LjCYC3, the homolog of K, was isolated but
no detectable mutation has been identified in a 5 kb
region containing the LjCYC3 gene in the kew1 mutant
(Wang et al., 2008).
In this study, we reported our effort to conduct large
scale mutagenesis by using physical-mutagenesis (γ-ray)
and chemical-mutagenesis (EMS) in L. japonicus. Two
new mutants, kew2 and kew3, possessing disrupted
shape or identity of lateral petal were isolated and cha-
racterized. Genetic analysis indicated that kew3 was
caused by single locus and allelic to the kew1. However,
kew2 was a variable mutant and display weaker mal-
function on the shape of lateral petals than kew1 or
kew3, suggesting another genetic locus might have in-
volved in the lateral petal development. With more
mutants and genetic loci were identified, the function of
the key regulators in the control of lateral petal deve-
lopment will be elucidated in the coming future.
1 Results
1.1 Physical-mutagenesis and chemical-mutagenesis
in Lotus japonicus
Physical-mutagenesis (γ-ray) and chemical-mutagenesis
(EMS) were used to construct the mutation library in L.
japonicus, respectively. Different dosages of muta-
genesis were evaluated by testing the germination rates,
and 50% germination rate was set as the limit dosage
for the treatment. Then, 25000 seeds of ecotype Gifu
were treated with γ-ray (250Gy) or EMS (0.75%)
respectively. The seeds were germinated and sown,
giving rise to about 20000 plants and 30000 plants in
two M1 populations in two growing seasons respectively.
Seeds were collected from each M1 plant and packed
separately. 13000 and 25000 M2 families were grown
in two separate growing periods in 2002 and 2005
respectively. Individual plants of the M2 generations,
were screened for development mutations. Several
floral mutations and leaf mutations were obtained and
selected for detailed analysis (data not shown).
1.2 Mutations possessing aberrant lateral petals
Two mutants involved in the malfunction of lateral
petal development were obtained in the γ-ray mutagenized
M2 population. These mutants displayed no other
detectable phenotype apart from their common chara-
cteristic: the lateral petals have abnormal shapes, while
the petals in dorsal and the ventral positions are as
normal as ones of the wild type. Since their phenol-
types mimic the one of kew1, they were designated as
kew2 and kew3 respectively (Figure 1c; Figure 1d).
When the shapes of lateral petals were compared
among kew1, kew2 and kew3, the subtle difference be-
tween kew1 and kew3 could be seen: there are wrinkles
at the edge of the kew3’s lateral petal; however, the shape
of kew2’s lateral petal is quite different from the one
of either kew1/kew3 or the wild type. It is evident that
the identity of lateral petals of kew1 and kew3 is altered,
which mimics the one of ventral petal in the wild type
(Figure 1a; Figure 1b and Figure 1d). In a comparison
with the wild type, the lateral petal of kew2 is na-
rrower and possesses a tip at the top end (Figure 1c).
Figure 1 Flowers of wild type and kew mutants in L. japonicus
Note: a: Awild type flower, b~d: Flowers of kew1, kew2 and kew3
mutants; D: Dorsal petal; L: Lateral petals; V: Ventral petals;
Arrows indicate the aberrant lateral petals in the kew mutants
1.3 Genetic analysis of kew2 and kew3
When kew3 was back-crossed with the wild type
parent line Gifu B129, all flowers of F1 are wild type,
while F2 progenitors gave wild type and mutant flowers
in 3:1 ratio (n>1500), indicating kew3 is caused by a
8