The PalWRKY77 transcription factor negatively regulates salt tolerance and abscisic acid signaling in Populus

Abstract

High salinity, one of the most widespread abiotic stresses, inhibits photosynthesis, reduces vegetation growth, blocks respiration and disrupts metabolism in plants. In order to survive their long-term lifecycle, trees, such as Populus species, recruit the abscisic acid (ABA) signaling pathway to adapt to a saline environment. However, the molecular mechanism behind the ABA-mediated salt stress response in woody plants remains elusive. We have isolated a WRKY transcription factor gene, PalWRKY77, from Populus alba var. pyramidalis (poplar), the expression of which is repressed by salt stress. PalWRKY77 decreases salt tolerance in poplar. Furthermore, PalWRKY77 negatively regulated ABA-responsive genes and relieved ABAmediated growth inhibition, indicating that PalWRKY77 is a repressor of the ABA response. In vivo and in vitro assays revealed that PalWRKY77 targets the ABA-and salt-induced PalNAC002 and PalRD26 genes by binding to the W-boxes in their promoters. In addition, overexpression of both PalNAC002 and PalRD26 could elevate salt tolerance in transgenic poplars. These findings reveal a novel negative regulation mechanism for the ABA signaling pathway mediated by PalWRKY77 that results in more sensitivity to salt stress in poplar. This deepens our understanding of the complex responses of woody species to salt stress.

The U‐box E3 ubiquitin ligase PalPUB79 positively regulates ABA‐dependent drought tolerance via ubiquitination of PalWRKY77 in Populus

“…This assay returned a total of seven proteins; remarkably, the WRKY transcription factor, PalWRKY77, had three hits, which suggested that it is a potential target protein of PalPUB79 (Figure 6a ). In a previous study, PalWRKY77 was found to negatively regulate tolerance to salt stress and the ABA response; more specifically, this protein inhibits the expression of PalNAC002 and PalRD26 transcription factors in poplars (Jiang et al ., 2020 ). To determine the interaction between PalPUB79 and PalWRKY77, we re‐constructed the vector expressing an AD‐PalWRKY77 fusion protein, and then subjected this protein to a point‐by‐point yeast two‐hybrid assay.…”

“…In Arabidopsis , high ABA levels can relieve AtWRKY40‐mediated repression of the ABA‐responsive genes, i.e., ABI4 and ABI5 , by translocating AtWRKY40 from the nucleus to the chloroplast envelope (Shang et al ., 2010 ). In our previous study on woody poplars, PalWRKY77 negatively regulated responses to salt stress and ABA signalling by directly binding to the W‐boxes of the promoters of PalNAC002 and PalRD26 to inhibit their expression (Jiang et al ., 2020 ). Although enhanced ABA levels have been shown to repress PalWRKY77 transcription, the mechanism through which ABA signalling removes the negative effect of PalWRKY77 in woody poplars remains unclear.…”

Molecular control to salt tolerance mechanisms of woody plants: recent achievements and perspectives

“…In addition, overexpression of two ABA signaling related NAC genes, PalNAC002 and PalRD26, enhanced salt tolerance in Populus alba var. pyramidalis (Jiang et al 2020). Taken together, these studies suggest that NAC family genes could improve salt tolerance in woody plants by different mechanisms, such as enhancing the ROS scavenging capacity, participating in ABA signaling and adjusting osmotic potential.…”

“…Therefore, WRKY might be used as a valid TF to improve or complement the production of plants tolerant to drought and salt stresses. Recently, Jiang et al (2020) isolated and characterized a WRKY gene in Populus alba var. pyramidalis.…”

Genome-Wide Identification of CBL-CIPK Gene Family in Honeysuckle (Lonicera japonica Thunb.) and Their Regulated Expression Under Salt Stress

“…Interestingly, W box (TTGACC) was identified in half of the CBL-CIPK genes from honeysuckle. W box is recognized by the family of WRKY transcription factors, which is involved in certain developmental processes and stress response, such as drought stress response in tomato ( Ahammed et al, 2020 ), salt response in Arabidopsis ( Xu et al, 2018 ) and populus ( Jiang et al, 2020 ). In general, the identified cis-acting elements here help in understanding their roles in the developmental and various biotic stress-related mechanisms.…”