Unravelling Cotton Nonexpressor of Pathogenesis-Related 1(NPR1)-Like Genes Family: Evolutionary Analysis and Putative Role in Fiber Development and Defense Pathway

The nonexpressor of pathogenesis-related 1 (NPR1) family plays diverse roles in gene regulation in the defense and development signaling pathways in plants. Less evidence is available regarding the significance of the NPR1-like gene family in cotton (Gossypium species). Therefore, to address the importance of the cotton NPR1-like gene family in the defense pathway, four Gossypium species were studied: two tetraploid species, G. hirsutum and G. barbadense, and their two potential ancestral diploids, G. raimondii and G. arboreum. In this study, 12 NPR1-like family genes in G. hirsutum were recognized, including six genes in the A-subgenome and six genes in the D-subgenome. Based on the phylogenetic analysis, gene and protein structural features, cotton NPR-like proteins were grouped into three different clades. Our analysis suggests the significance of cis-regulatory elements in the upstream region of cotton NPR1-like genes in hormonal signaling, biotic stress conditions, and developmental processes. The quantitative expression analysis for different developmental tissues and fiber stages (0 to 25 days post-anthesis), as well as salicylic acid induction, confirmed the distinct function of different cotton NPR genes in defense and fiber development. Altogether, this study presents specifications of conservation in the cotton NPR1-like gene family and their functional divergence for development of fiber and defense properties.