Exploration of senescence-regulatory genes for extension of the greening period in Zoysia japonica through transcriptome analysis of leaf senescence

Abstract

In this study, I performed comparative transcriptome analysis to understand senescence responses triggered by age, dark, and salt through a high-throughput RNA sequencing in Z. japonica. The differentially expressed genes (DEGs) which responded to dark, salt, or age-induced senescence accounted for 23.46, 17.60, and 3.88% among expressed genes, respectively, and the DEGs which commonly responded to all three conditions (cDEGs) accounted for 2.13%. Gene set enrichment analysis for functional characterization of the transcriptome during senescence revealed many convergent and distinct biological processes were required for each senescence response; for example, “degradation of fatty acid and amino acid” were commonly affected in all senescence conditions, while “programmed cell death (PCD) system”, “biosynthesis and degradation processes of hemicellulose” and “primary active transport of solute” were specifically enriched of age-, dark-, and salt-induced senescence, respectively. I also found that NAC, WRKY, bHLH, and ARF were major DEG TFs groups that are involved in the transcriptional regulation of DEGs during leaf senescence. Transient expression of ZjNAP, ZjWRKY75, ZjARF2, ZjNAC1, ZjNAC083, ZjARF1, and ZjPIL5 as effectors in protoplasts altered the expression of senescence promoter-driven LUC reporters, indicating that these TF cDEGs likely to function as senescence regulators. Additionally, functional activity of ZjNAC and ZjNAP in senescence regulation were validated in dark-induced senescence assay in tobacco leaves through their transient expression. Overall, this study will provide new insights into molecular mechanisms of Z. japonica leaf senescence and potential gene resources to improve the economic value of Z. japonica by extending the leaf greening period.