Functional analysis of nine cotton genes related to leaf senescence in Gossypium hirsutum L.

Leaf senescence is defined as a deterioration process that continues to the final developmental stage of leaf. This process is usually regulated by both external and internal factors. There are about 5356 senescence associated genes belonging to 44 plant species. A great number of these genes were identified in Arabidopsis. Leaf senescence can be regulated by many transcription factors. In this study, nine gene families were selected according to their expression levels during leaf senescence from our laboratory database. Phylogenetic tree was constructed by MEGA6. Cultivated cotton CCRI-10 seeds were sown in the experimental field of Institute of Cotton Research of CAAS for profiling and leaf development stages analysis. For abiotic (drought and salt) stress and phytohormone (ABA, SA, ET and JA) treatments, CCRI-10 seeds were sown in potting soil at 25 °C in a chamber room. Total RNA was isolated from various samples and the cDNA prepared for qRT-PCR. The comparative CT method was applied to calculate the relative expression levels of genes. For phylogenetic tree, nine cotton genes were divided into two groups, most of homologous genes in previous studies showed roles in phytohormones and abiotic stress. Expression profiling of the nine genes showed different patterns of tissue specific expression. In leaf development stages, majority of cotton genes showed high expression in early and complete senescence stage. Furthermore, most of cotton genes have positive or negative response to phytohormones and abiotic stress. Based on the results of this study, we found four cotton genes CotAD_07559, CotAD_37422, CotAD_21204 and CotAD_54353 as candidate genes for leaves senescence and abiotic stress.