Genome-wide identification of Lhcb gene family and functional characterization of BcLhcb1.2 for cold tolerance in non-heading Chinese cabbage.

The light-harvesting chlorophyll a/b binding protein (Lhcb) constitutes the antenna system of photosystem II (PSII), which also plays an important role in plant growth and responses to abiotic stress. However, the role of Lhcb genes in cold stress remains poorly characterized in non-heading Chinese cabbage. Here, 25 BcLhcb genes were identified and classified into 8 subfamilies, and these genes were mapped to nine chromosomes. Analysis indicated that BcLhcb genes may respond to hormonal and abiotic stress. Subcellular localization and expression pattern demonstrated that BcLhcb1.2, a chloroplast-localized gene, was significantly induced by cold stress. When BcLhcb1.2 was silenced, weaker cold tolerance was found than in control. And cold-responsive genes were more significantly down-regulated in BcLhcb1.2 silent lines. In overexpression assays, lower malondialdehyde content and higher proline content showed that BcLhcb1.2 enhanced cold tolerance of Arabidopsis thaliana, while lhcb1 weakened. Moreover, the abscisic acid sensitivity was higher in overexpressing lines and lower in the lhcb1 line, indicating that BcLhcb1.2 participated in the ABA signaling pathway. BcABF4, an ABA-responsive transcription factor, was identified which could bind the ABRE box in BcLhcb1.2 promoter and activate its expression. In summary, a novel regulatory model, ABA-BcABF4-BcLhcb1.2, was proposed to enhance cold tolerance. It provides new insights for resistance breeding in non-heading Chinese cabbage.