Systematic identification and expression analysis of BREVIS RADIX-like homologous genes in rice

BREVIS RADIX is a novel plant-specific gene family with highly conserved protein sequences; the key member of this family, BRX, controls cell proliferation and root elongation in Arabidopsis. In this study, six members of rice BRX-like gene family containing the conserved BRX domain were identified in japonica rice. Phytogenetic analysis suggested that BRX-like genes may be evolved before the divergence of vascular plant and bryophytes species. Four rice BRX-like genes were predominantly (OsBRXL1, OsBRXL2, and OsBRXL4) or specifically (OsBRXL3) expressed in young panicle. Except one member (OsBRXL6) that was not expressed in all the tissues and organs investigated, the other five genes were differentially responsive to major stresses including drought, salt, and cold, suggesting that the BRX-like family may also function in abiotic stress responses. OsBRXL1 and OsBRXL4 were significantly up-regulated by brassinosteroid and auxin, respectively. To further test the function of BRX-like genes in rice, the OsBRXL4 was overexpressed in rice Zhonghua 11. The OsBRXL4-overexpression plant showed significantly longer root and increased sensitivity to auxin than wild type, suggesting that OsBRXL4 may be involved in primary root growth through the auxin signaling pathway.