The allene oxide synthase gene family in sugarcane and its involvement in disease resistance

Allene oxide synthase (AOS), one of the key enzymes in the jasmonic acid (JA) biosynthesis pathway, has been well documented in enhancing plant adaptability to the external environment, but has not yet been reported in sugarcane (Saccharum spp.). Here, eight SsAOS and 36 SoAOS genes were identified from the genomes of sugarcane wild species S. spontaneum and sugarcane tropical species S. officinarum, respectively. The phylogenetic tree showed that AOSs from different plant species were clustered into four groups, including 13-AOS, 9-AOS, 9/13-AOS type Ⅰ, and 9/13-AOS type Ⅱ. Evolutionary analysis revealed that the AOS gene family was relatively conserved in structure, but has diverse evolutionary mechanisms in S. spontaneum and S. officinarum. Cis-regulatory elements and expression pattern analysis demonstrated that SsAOSs were involved in various defensive responses which included smut stress caused by Sporisorium scitamineum. Due to the excellent performance of SsAOS1a and SsAOS1b under S. scitamineum stress, their homologous gene ShAOS1 (GenBank Accession Number: MK674850) which encoded a non-secretory acid-stable hydrophilic 9/13-AOS protein and located at the plasma membrane was isolated from a sugarcane hybrid variety YC05-179 that was inoculated with S. scitamineum for 2 d. The transcripts of ShAOS1 were up-regulated under methyl jasmonate, salicylic acid, and abscisic acid treatments. Transient overexpression of the ShAOS1 gene in Nicotiana benthamiana could promote hydrogen peroxide accumulation and induce immune-related genes expression. Furthermore, genetic transformation and RNA-sequencing (RNA-seq) analysis showed that the stable overexpression of the ShAOS1 gene enhanced the resistance of transgenic N. benthamiana plants to Fusarium solani var. coeruleum through the modulation of lots of transcription factors and protein kinases, a series of stimulus response processes and signalling pathways. These results provide the theoretical basis and candidate target genes for sugarcane disease resistance molecular breeding.