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.

Heat stress induces expression of a set of thermotolerance-related genes in plants. We focused on rice (Oryza sativa L.) homologs of the gene family that encodes galactinol synthase (OsGolS), which is closely related to the Arabidopsis thaliana galactinol synthase (AtGolS) family whose expression is induced under various stresses. OsGolS1 was highly up-regulated compare to the level of OsGolS2 in re- sponse to heat stress. Interestingly, OsGolS1 was also up-regulated by treatment with the Hsp90 inhibitor, geldanamycin (GDA). Expression profiles of OsGolS1 were correlated to those of OsHsfA2 under the GDA treatments. Treatment with GDA increased expression of OsHsfA2, but marginally increased or did not change OsHsfA1 expression. Notably, gel shift assay indicated that OsHsfA2 binds directly to OsGolS1 promoter region and that OsHsfA1 also binds to the promoter regions of OsHsfA2. Both OsHsfA2 and OsGolS1 were dramatically induced in response to heat stress. Accordingly, galactinol and raffinose contents in rice seedlings increased significantly following the induction of OsGolS1. Pre-treatment of rice seedlings with raffinose or GDA improved their thermotolerance. These results suggest that OsGolS1 plays an important role in response to heat stress, possibly via the transcription cascade of OsHsfA1-OsHsfA2 that leads to galactinol and raffinose accumulation, and that the increased content of these carbohydrates is a