The function and regulatory network of sugarcane chitinase gene ScChiIV1 in response to pathogen stress
Plant chitinase is a pathogenesis-related protein that can hydrolyze chitin, the main component of fungal cell walls, and plays an important role in plant disease defense responses. Our previous study found the sugarcane class IV chitinase gene ScChiIV1 (GenBank Accession No.: KP165001) was responding positively to smut pathogen Sporisorium scitamineum stress, but its disease resistance function and mechanism were unclear. Here, the upstream promoter of the ScChiIV1 gene (pro-ScChiIV1) with a length of 1696 bp was cloned which contained cis-acting elements related to hormone and stress response. Transient overexpression of the pro-ScChiIV1 in Nicotiana benthamiana showed inducible transcriptional levels by ABA, Fusarium solani var. coeruleum, and Alternaria longipes stimuli. Furthermore, stable overexpression of the ScChiIV1 gene in N. benthamiana enhanced the resistance of transgenic plants against F. solani var. coeruleum and S. scitamineum. Phenotypic monitoring, relevant physiological indicators, immune-related gene expression, and transcriptome analyses revealed that ScChiIV1 may activate potential TFs and PKs by inducing Ca2+ influx, ROS generation, and MAPK activation, thereby increasing the expression level of genes related to hormone signaling pathways, hypersensitive response (HR), and reactive oxygen species (ROS), as well as the activities of chitinase, superoxide dismutase (SOD), and catalase (CAT). In addition, ScChiIV1 reduced the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA) in transgenic plants, ultimately increasing disease resistance. This study provides novel insights into the molecular mechanism of the early response of the ScChiIV1 gene to pathogen stress and offers an excellent genetic resource for sugarcane disease resistant breeding.