Abstract:

To elucidate the mechanism underlying development of leaf marginal lobes in pakchoi，an LOM2 homologous gene，BrLOM2，was isolated respectively from near-isogenic lines with and without lobed leaves in pakchoi using the homology-based cloning methods. The BrLOM2 gene contains an open reading frame of 549 bp in length encoding a protein of 182 amino acids. Sequence analysis showed that the BrLOM2 protein contained conservative structure domains of the GRAS family. The BrLOM2 sequence from genomic DNA showed no intron and phylogenetic analysis suggested that BrLOM2shares high homology with known LOMs from other plant species. Moreover，the putative BrLOM2 protein was closely clustered with several Brassica LOMs. qRT-PCR analysis revealed that BrLOM2gene has higher expression in leaves and shoot apexes，and lower expression in flowers. Further more，BrLOM2 gene has higher expression level in pakchoi lines with smooth leaves than in the lines with lobed leaves. The expression of BrLOM2 in pakchoi lines with lobed leaves became higher，while the number of lobes in them had the synchronized trend. In leaves，the expression of BrLOM2 was affected by application of exogenous GA₃ and 6-BA hormone treatments. Interestingly，GA₃ treatment increased the BrLOM2gene expression，whereas 6-BA treatment decreased it. In summary，the above-mentioned results indicated that the reduced transcriptional expression of BrLOM2 gene was the major factor contributing to leaf marginal lobes.

Key words: Brassica rapa ssp. chinensis, LOM2, lobed leaf, gene clone, expression pattern