Leaf senescence is a complex and precise regulatory process that is correlated with numerous internal and environmental factors. Leaf senescence is tightly related to the redistribution of nutrients, which significantly affects productivity and quality, especially in crops. Evidence shows that the mediation of transcriptional regulation by WRKY transcription factors is vital for the fine‐tuning of leaf senescence. However, the underlying mechanisms of the involvement of WRKY in leaf senescence are still unclear in wheat. Using RNA sequencing data, we isolated a novel WRKY transcription factor, TaWRKY40‐D, which localizes in the nucleus and is basically induced by the progression of leaf senescence. TaWRKY40‐D is a promoter of natural and dark‐induced leaf senescence in transgenic Arabidopsis thaliana and wheat. We also demonstrated a positive response of TaWRKY40‐D in wheat upon jasmonic acid (JA) and abscisic acid (ABA) treatment. Consistent with this, the detached leaves of TaWRKY40‐D VIGS (virus‐induced gene silencing) wheat plants showed a stay‐green phenotype, while TaWRKY40‐D overexpressing Arabidopsis plants showed premature leaf senescence after JA and ABA treatment. Moreover, our results revealed that TaWRKY40‐D positively regulates leaf senescence, possibly by altering the biosynthesis and signalling of JA and ABA pathway genes. Together, our results suggest a new regulator of JA‐ and ABA‐related leaf senescence, as well as a new candidate gene that can be used for molecular breeding in wheat.
Leaf senescence is crucial for crop yield and quality. Transcriptional regulation is a key step for integrating various senescence-related signals into the nucleus. However, few regulators of senescence implicating transcriptional events have been functionally characterized in wheat. Based on our RNA-seq data, we identified a WRKY transcription factor, TaWRKY13-A, that predominately expresses at senescent stages. By using the virus-induced gene silencing (VIGS) method, we manifested impaired transcription of TaWRKY13-A leading to a delayed leaf senescence phenotype in wheat. Moreover, the overexpression (OE) of TaWRKY13-A accelerated the onset of leaf senescence under both natural growth condition and darkness in Brachypodium distachyon and Arabidopsis thaliana. Furthermore, by physiological and molecular investigations, we verified that TaWRKY13-A participates in the regulation of leaf senescence via jasmonic acid (JA) pathway. The expression of JA biosynthetic genes, including AtLOX6, was altered in TaWRKY13-A-overexpressing Arabidopsis. We also demonstrated that TaWRKY13-A can interact with the promoter of AtLOX6 and TaLOX6 by using the electrophoretic mobility shift assay (EMSA) and luciferase reporter system. Consistently, we detected a higher JA level in TaWRKY13-A-overexpressing lines than that in Col-0. Moreover, our data suggested that TaWRKY13-A is partially functional conserved with AtWRKY53 in age-dependent leaf senescence. Collectively, this study manifests TaWRKY13-A as a positive regulator of JA-related leaf senescence, which could be a new clue for molecular breeding in wheat.
SUMMARY Leaf senescence involves massive multidimensional alterations, such as nutrient redistribution, and is closely related to crop yield and quality. No apical meristem, Arabidopsis transcription activation factor, and Cup‐shaped cotyledon (NAC)‐type transcription factors integrate various signals and modulate an enormous number of target genes to ensure the appropriate progression of leaf senescence. However, few leaf senescence‐related NACs have been functionally characterized in wheat. Based on our previous RNA‐sequencing (RNA‐seq) data, we focused on a NAC family member, TaNAC69‐B, which is increasingly expressed during leaf senescence in wheat. Overexpression of TaNAC69‐B led to precocious leaf senescence in wheat and Arabidopsis, and affected several agricultural traits in transgenic wheat. Moreover, impaired expression of TaNAC69‐B by virus‐induced gene silencing retarded the leaf senescence in wheat. By RNA‐seq and quantitative real‐time polymerase chain reaction analysis, we confirmed that some abscisic acid (ABA) biosynthesis genes, including AAO3 and its ortholog in wheat, TraesCS2B02G270600 (TaAO3‐B), were elevated by the overexpression of TaNAC69‐B. Consistently, we observed more severe ABA‐induced leaf senescence in TaNAC69‐B‐OE wheat and Arabidopsis plants. Furthermore, we determined that TaNAC69‐B bound to the NAC binding site core (CGT) on the promoter regions of AAO3 and TaAO3‐B. Moreover, we confirmed elevated ABA levels in TaNAC69‐B‐OE wheat lines. Although TaNAC69‐B shares 39.83% identity (amino acid) with AtNAP, TaNAC69‐B did not completely restore the delayed leaf senescence in the atnap mutant. Collectively, our results revealed a positive feedback loop, consisting of TaNAC69‐B, ABA biosynthesis and leaf senescence, that is essential for the regulation of leaf senescence in wheat.
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