Isolation and Characterization of an Ethylene Biosynthesis Gene in Response to Waterlogging in Chrysanthemum

Waterlogging has major effects on natural vegetation and agricultural crops, resulting in retardation of growth and development of many plants mainly in humid regions. The phytohormone ethylene is known to mediate a diverse array of signaling processes during abiotic stress in plants. To better understand the roles of ethylene in response to waterlogging, a full-length CgACO cDNA (GenBank accession KT438660) was isolated from chrysanthemum and its expression patterns were examined in two Chrysanthemum species (Chrysanthemum zawadskii and C. nankingense) with differ tolerance to waterlogging. In the sensitive one (C. nankingense), the transcriptional levels of the CgACO were increased rapidly but only transiently (12 hrs after treatment) in the roots. In tolerant one (C. zawadskii), the expression of the CgACO was increased rapidly and maintained up to 48 hrs post-treatment. CgACO expression was not induced by exogenous ethylene application in both species. The ethylene inhibitor, 1-methylcyclopropene (1-MCP), enhanced CgACO expression after 12h of waterlogging in tolerant one but much less in the sensitive species. Higher expression of the CgACO gene correlated with higher accumulation of ethylene in the tolerant C. zawadskii. This supports the previously observed phenomenon that C. zawadskii exhibits well-developed aerenchyma adaptations to cope with waterlogged conditions.