Genome-wide analysis of the B3 transcription factors reveals that RcABI3/VP1 subfamily plays important roles in seed development and oil storage in castor bean (Ricinus communis).

The B3 transcription factors (TFs) in plants play vital roles in numerous biological processes. Although B3 genes have been broadly identified in many plants, little is known about their potential functions in mediating seed development and material accumulation. Castor bean (Ricinus communis) is a non-edible oilseed crop considered an ideal model system for seed biology research. Here, we identified a total of 61 B3 genes in the castor bean genome, which can be classified into five subfamilies, including ABI3/VP1, HSI, ARF, RAV and REM. The expression profiles revealed that RcABI3/VP1 subfamily genes are significantly up-regulated in the middle and later stages of seed development, indicating that these genes may be associated with the accumulation of storage oils. Furthermore, through yeast one-hybrid and tobacco transient expression assays, we detected that ABI3/VP1 subfamily member RcLEC2 directly regulates the transcription of RcOleosin2, which encodes an oil-body structural protein. This finding suggests that RcLEC2, as a seed-specific TF, may be involved in the regulation of storage materials accumulation. This study provides novel insights into the potential roles and molecular basis of B3 family proteins in seed development and material accumulation.

Proposal of Intrasporangium mesophilum sp. nov., and reclassification of Humihabitans oryzae Kageyama et al. 2007 as Intrasporangium oryzae comb. nov.

A gram-positive and aerobic bacterium, designated strain YIM 49065(T), was isolated from rhizospheric soil of Jatropha curcas in Yunnan, China. This isolate formed branched and fragmented mycelia containing ll-diaminopimelic acid as the diagnostic diamino acid in the cell-wall peptidoglycan. The major cellular fatty acid profile was characterized by iso-C(14 : 0), iso-C(15 : 0) and iso-C(16 : 0), and the predominant menaquinone was MK-8(H(4)). The DNA G+C content was 69.6 mol%. A phylogenetic analysis based on 16S rRNA gene sequence demonstrated that strain YIM 49065(T) was closely associated with Intrasporangium calvum DSM 43043(T) and Humihabitans oryzae KV-657(T), exhibiting 98.8 % and 98.6 % 16S rRNA gene sequence similarities, respectively. Furthermore, DNA-DNA hybridizations among strains YIM 49065(T), I. calvum DSM 43043(T) and H. oryzae DSM 22331(T) indicated that this isolate represented a novel species in the genus Intrasporangium. On the basis of these data, we proposed one novel species, Intrasporangium mesophilum sp. nov., for strain YIM 49065(T) ( = DSM 23217(T)  = CCTCC AA 209077(T)). Additionally, the comparison of biochemical and phylogenetic characters supported the reclassification of Humihabitans oryzae as a separate species within the genus Intrasporangium, Intrasporangium oryzae comb. nov. (type strain KV-657(T)  = JCM 15924(T)  = NBRC 101802(T)  = NRRL B-24470(T)).