Identification and Expression Analysis of Two allene oxide cyclase (AOC) Genes in Watermelon

Abstract

Allene oxide cyclase (AOC, EC 5.3.99.6) catalyzes the most important step in the jasmonic acid (JA) biosynthetic pathway and mediates plant defense response to a wide range of biotic and abiotic stresses. In this study, two AOC genes were identified from watermelon. Sequence analysis revealed that each of ClAOC1 and ClAOC2 contained an allene oxide cyclase domain and comprised eight highly conserved β-strands, which are the typical characteristics of AOC proteins. Phylogenetic analysis showed that ClAOC1 and ClAOC2 were clustered together with AOCs from dicotyledon, with the closest relationships with JcAOC from Jatropha curcas and Ljaoc1 from Lotus japonicus. Different intron numbers were observed in ClAOC1 and ClAOC2, which may result in their functional divergence. qRT-PCR analysis revealed that ClAOC1 and ClAOC2 have specific and complex expression patterns in multiple organs and under hormone treatments. Both ClAOC1 and ClAOC2 displayed the highest transcriptional levels in stem apex and fruit and exhibited relatively lower expression in stem. JA, salicylic acid (SA), and ethylene (ET) could enhance the expression of ClAOC1 and ClAOC2, particularly that of ClAOC2. Red light could induce the expression of ClAOC2 in root-knot nematode infected leaf and root of watermelon, indicating that ClAOC2 might play a primary role in red light-induced resistance against root-knot nematodes through JA signal pathway. These findings provide important information for further research on AOC genes in watermelon.