Abstract
Among APETALA2 (AP2)-type plant specific transcription factor family, WRINKLED1 (WRI1), has appeared to be a master gene transcriptionally regulating a set of carbon metabolism- and fatty acid synthesis (FAS)-related genes responsible for seed specific triacylglycerols (TAGs) storage in oil plants. B3 type transcription factors, such as ABI3 and FUS3, are known to be involved in seed development, such as seed storage protein synthesis and maturation. Based on the recent whole genome sequence data of castor bean (Ricinus communis L.), putative WRI1 homologs (RcWRI1, RcWRI2) specifically expressed in castor bean seed have been identified by comparing organ specific expression profiles among seed development-related transcription factors, seed storage specific genes (Ricin, RcOleosin) and a set of FAS genes including genes for sucrose synthase (RcSUS2), biotin carboxyl carrier protein (a subunit of acetyl-CoA carboxylase, RcBCCP2) and ketoacyl-acyl carrier protein synthase (RcKAS1). Immunoreactive signals with WRI1, FUS3 and ABI5-related polypeptides were also detected in seed specifically, consistent with the expression profiles of seed development-related genes. The WRI1 binding consensus sites, [CnTnG](n)(7)[CG], designated as the AW-box, were found at the promoter region of RcBCCP2 and RcKAS1. Thus, RcWRI1 possibly play a pivotal role in seed specific TAGs storage during seed development by directly activating FAS -related genes.
Highlights
The castor bean plant is a tropical shrub that is one of the most important and valued oilseed crops
It is possible that RcWRI1 belonging to the same clade of AtWRI1 and ZmWRI1 plays an important role in seed specific expression of fatty acid synthesis (FAS) genes, because AtWRI1 and ZmWRI1 appeared to promote the master regulation of a set of FAS-related genes [8,18]
It was reported that AtWRI1 binds to a specific sequence motif, AW-box, in the promoter regions of BCCP2 and KAS1 and other FAS genes [9]
Summary
The castor bean plant is a tropical shrub that is one of the most important and valued oilseed crops. It has been proposed that castor bean has a potential to produce biodiesel, because of its unique properties that the seed has high oil content, toxic storage protein (ricin) confers oil source without competition to food resource and the plant can tolerate to severe environments where food crops are unfavorable [3]. Genetic and molecular biological studies using Arabidopsis thaliana have currently unveiled that a set of specific transcription factors are temporarily and spatially expressed during the seed development and its maturation and that those seed specific transcription factors collaborate in regulation of seed specific genes for storage proteins and TAGs synthesis [8,9]. At the downstream of LEC1, LEC2, ABI3 and FUS3 form a complicated network interacting to each other to AJPS
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