Expression Characteristics of LSH Genes in Brassica Suggest their Applicability for Modification of Leaf Morphology and the Use of their Promoter for Transgenesis

The functions of DUF640/ALOG (Arabidopsis LSH1 and Oryza G1) domain proteins, which are found in most land plants, have not been well characterized, but some of these proteins regulate inflorescence architecture in rice and specify organ boundaries in Arabidopsis. Arabidopsis DUF640-domain genes are initially identified as LIGHT-SENSITIVE HYPOCOTYLS (LSH) genes. Chinese cabbage leaves have large, white midribs and photosynthetic leaf blades (or lamina). A DUF640 domain gene of Brassica rapa, BrLSH2, is specifically expressed in the midrib of Chinese cabbage. Arabidopsis and rice possess ten LSH family genes, but B. rapa has 24 LSH genes, which can be categorized into two or four groups based on sequence identity. Here, we examined the expression patterns of the LSHs in various Brassica species and analyzed the promoter sequence of the BrLHS2 gene. The transcript levels of most LSH genes were very high in the midrib but low in the leaf blade. These genes were evenly expressed throughout the petiole region of Korean cabbage and highly expressed in the leaf base region near the stem and in the border area in B. oleracea. In addition, BrLSHs were expressed in both bundle and mesophyll cells of the midrib. These expression patterns suggest the possible use of these genes to generate leafy vegetables with altered leaf morphology. The BrLSH2 promoter, which contains auxin- and cytokinin-responsive elements as well as leaf development-related elements, may confer midrib-specific expression, suggesting that this promoter may be useful for the production of midrib-targeted transgenic Chinese cabbage.