LecRK-Ⅷ.2 mediates the cross-talk between sugar and brassinosteroid during hypocotyl elongation in Arabidopsis

Sugars and phytohormones co-regulate various common responses and development processes in plants. The previous studies reveal that the cross-talk between sugar and phytohormone signaling affects cellular elongation in root and hypocotyl. The elongation of hypocotyl is vital for the initial growth and development of seedlings during the transit from skotomorphogenesis to photomorphogenesis. Here, we found that LecRK-Ⅷ.2 gene regulated hypocotyl elongation involving in cross-talk between sugar and BR signaling. The results showed that sugar treatment could partly recover the defect of brassinosteroid (BR) response in bak1 mutant. LecRK-Ⅷ.2 gene regualted hypocotyl elongation by integrating the signaling cross-talk among BR, sucrose, glucose and fructose. Expression analysis of BR signaling related genes in response to exogenous sugar and BR suggested that LecRK-Ⅷ.2 may play essential roles in regulating hypocotyl growth. We also studied the roles of sugar transporter genes (STP1 and STP13) during hypocotyl elongation in the lecrk-Ⅷ.2 mutants in response to sugar/BR. The results showed that STP1 and STP13 expression in lecrk-Ⅷ.2-1 mutants were higher than that of Col-0 plant under sugar-free conditions. The expressions of STP1 in lecrk-Ⅷ.2 mutants were down-regulated compared to Col-0 under glucose treatments. The expressions of STP13 in lecrk-Ⅷ mutants were up-regulated compared to Col-0 under sucrose treatments. Altogether, our work indicated that LecRK-Ⅷ.2 regulated hypocotyl elongation by mediating the signaling cross-talk among sucose, glucose and BR.