Ethylene induced stay-green gene expression regulates drought stress in wheat

Abstract

Stay-green is an integrated drought adaptation trait characterized by a green leaf phenotype during grain filling under terminal drought. Ethylene is the key hormone for regulating the leaf senescence pathway under natural and stress conditions. The present study was conducted to assess the associative function of ethylene in regulating chlorophyll degrading enzymes viz., chlorophyllase (TaCHLase) and pheophorbide a oxygenase (TaPaO) in wheat (Triticum aestivum L.) under drought stress. Three wheat genotypes (HW 4059, HW 4022 and HW 2078) differing in drought tolerance efficiency were subjected to drought stress for ten days at the reproductive stage. A decline in stay-green traits was found in susceptible genotypes (HW 4059) with yield losses compared to tolerant ones (HW 4022 and HW 2078). The expression level of TaCHLase1 and TaPaO was higher in susceptible genotypes than tolerant ones under drought/osmotic stress. Ethylene upregulated, while ethylene inhibitors downregulated the gene expression. In this study, a novel gene annotated as TaCHLase1 was cloned. The complete cDNA sequence of TaCHLase1 is composed of 1054 bp nucleotides containing an open reading frame of 960 bp encoding 319 amino acids. The encoded protein contained conserved residues such as lipase motif GXSXGG at position 143-148 and putative active site Ser145. Sequence alignment showed TaCHLase1 shares a higher degree of identity with other species. The result suggested that ethylene upregulates the expression of TaCHLase1 gene, inducing chlorophyll degradation. The study further helps in understanding the mechanism of stay-green trait-induced drought tolerance mechanism in wheat.