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A. Functional genomics on seed development
Crop seeds contribute major calories and nutrition to human. To increase the yield and nutrition,
understanding the mechanism of seed formation is essential. Seed development involves
embryogenesis and endosperm development, a complex and orchestrated process that involves
many gene functions and is vital to reproduction of plants. We are interested in
1) functional analysis of the genes that regulate seed development;
2) elucidation of carotenoid catabolism mechanism in seeds.
1. Genetic and functional dissection of genes regulating maize seed development.
Using maize as a model system, we have
A
B
C
isolated small kernel (smk) and embryo
defective mutants (emb) by using the
Robertson’s Mutators as mutagens.
Recently we have cloned several genes
that are important to embryogenesis. Loss
emb12
emb12
WT
Emb12b
of function in these genes causes embryo
Emb12c
Transposon insertion sites
Emb12a
development arrested at transition stage
Emb12
(Fig.
1).
Using
approaches
of
biochemistry, genetics and molecular
Fig. 1. Arrested embryo development in emb12. mutant
and the emb12 gene structure.
biology, we are attempting to decipher
their functions.
2. Provitamin A nutrition accumulation in crop seeds
Carotenoids are the precursors of Vitamin A, a nutrient essential to the development of
immune system and eye particularly in children. Vitamin A deficiency is a major problem in
developing countries. One way to combat this problem is to create crop grains with fortified
carotenoid contents. As manifested in the Golden Rice (Paine et al., 2005; Ye et al., 2000),
introducing carotenoid synthetic genes increases carotenoid accumulation.
Our work on White cap demonstrated that
carotenoid catabolism (degradation) also plays
an important role in carotenoid accumulation in
seeds. White cap locus is a dominant mutant
conferring carotenoid deficient phenotype (Fig.
2a). Molecular cloning demonstrated that Wc
contains a tandem array of a gene encoding
carotenoid cleavage dioxygenase 1 (CCD1).
CCD1 is capable to degrade a broad spectrum
of carotenoids (fig. 2b). From analyses of CCD
genes in other species, it appears that this
degradation pathway is conserved in plants.
This opens the possibility to modify the Golden
Rice to accumulate more provitamin A. In
addition, we also attempt to elucidate the
biological function of CCD1 gene and the
mechanism of the tandem array creation.
A
B
ZmCCD1
-
+
Zeaxanthin
C
-
+
-
β-carotene
+
Lycopene
ZmCCD1 activity in E. coli cells
β-carotene
O
O
+
O
Dominant Wc
(b-ionone)
C14 dialdehyde
O
+
(b-ionone)
Fig. 2. Wc encodes a ZmCCD1 protein involved in the
degradation of carotenoids in maize seeds.
B. Regulation of abscisic acid biosynthesis
To establish the abscisic acid (ABA) biosynthesis pathway in plant, we cloned and analysed
the function of VP14, which is a key gene in ABA biosynthesis pathway.