Analysis of Lhcb gene family in rapeseed (Brassica napus L.) identifies a novel member “BnLhcb3.4” modulating cold tolerance

The light-harvesting chlorophyll a/b-binding proteins (Lhcb) constitute the antenna system of the photosynthetic apparatus that has an essential function in photosynthesis and modulating stress responsiveness. In this study, we identified 35 Lhcb genes (BnLhcbs) in the rapeseed (Brassica napus L.) genome, which were clustered into 8 groups. The BnLhcb genes were distributed on 15 chromosomes of rapeseed; the subsequent analysis of gene structures showed that these members were highly conserved. Based on the importance of Lhcbs for plant defense against abiotic stresses, responses of BnLhcbs to cold stress were analyzed using cold-tolerant and -sensitive rapeseed cultivars. The BnLhcb genes exhibited distinct expression patterns, among which, BnLhcb3.4 was dramatically induced in the tolerant cultivar and down-regulated in the sensitive cultivar. Furthermore, the cDNA sequences of the BnLhcb3.4 gene was successfully cloned, the subcellular investigation confirmed that BnLhcb3.4 localized in chloroplast. The transgenic analysis indicated that overexpression of the BnLhcb3.4 gene significantly enhanced the freezing tolerance of transgenic Arabidopsis, together with increased abscisic acid (ABA) sensitivity. In addition, a set of ABA-responsive genes were altered in the transgenic plants. Taken together, these data demonstrate that BnLhcb3.4 may contribute to cold tolerance by evolving ABA signaling pathway.