Effects of exogenous methyl-jasmonate on the morphology, hormone status, and gene expression of developing lateral roots in Malus hupehensis

Abstract Malus hupehensis is regarded as a superior rootstock in China. In this study, in order to investigate the mechanism by which MeJA promotes and affects lateral root (LR) development, M. hupehensis seedlings were treated with exogenous applications of 1 μM methyl-jasmonate (MeJA). Results indicated that MeJA treatment promoted LR development, but inhibited shoot development. MeJA treatment increased the levels of both endogenous auxin (IAA) and zeatin-riboside (ZR), and reduced gibberellin (GA1+3). Additionally, a significant upregulation in the expression of MdCOI1, MdMYC2 and MdJDL1 were also observed in response to the MeJA treatment. Although transcript levels of key IAA synthesis related genes increased, but those genes related to IAA transport were declined, which corresponded with higher IAA levels in the MeJA-treated samples. The expression of MdIAA5, which is a negative regulator of MdARF7, was dramatically downregulated in MeJA-treated apple seedlings, resulted in elevated expression of MdLBD16 and MdLBD29. Additionally, the expression of MdCYCD3;1 and MdCYCP4;1 were induced, which in turn increased LR development. Collectively, MeJA treatment increased the number of LRs and other growth characteristics.