Cloning of the key genes in maize oxylipins pathways and their roles in herbivore induced defense

Abstract

To gain an understanding of the molecular basis of signaling pathways in herbivore-induced maize plant defense, three key genes,ZmAOS, ZmAOC andZmHPL, which are involved in the biosynthesis of oxylipin signals, have been cloned using RT-PCR in this study. Beet armyworm (BAW) infestation induced the systemic expression of the key genes involved in the biosynthesis of oxylipin signals similar to exogenous methyl jasmonate (MeJA). Moreover, the systemic expression patterns of maize defense-related genes were similar between maize leaves induced by jasmonic acid (JA) and damaged by BAW. Previous treatment with salicyhydroxamic acid (SHAM), an inhibitor of jasmonates (JAs) signal pathway followed by BAW infestation did not induce the systemic expression of the defense-related genes. Exposure to the vapors of green leafy volatiles (GLVs, (Z)-3-hexen-1-ol, (E)-2-hexenal, (E)-3-hexenal) and β-ocimene induced the expression of the defense-related genes, as well as the key genes involved in biosynthesis of JAs. However, previous treatment with SHAM clearly decreased the transcript levels of the defense genes induced by (Z)-3-hexen-1-ol, (E)-2-hexenal and (E)-3-hexenal. These results demonstrate the major role of oxylipin signal pathway in herbivore-induced maize chemical defense. JA was the endogenous signal in the process of herbivore-induced maize systemic defense. GLVs, another group of oxylipin, played an important role in the process of herbivore-induced systemic defense outside the plant. Furthermore, the expression of defense-related genes induced by GLVs was partially dependent on JAs signal pathway, while β-ocimene induction was independent of JAs signal pathway.