Drought attenuates plant defence against bacterial pathogens by suppressing the expression of CBP60g/SARD1 during combined stress

Abstract

In nature, plants are frequently exposed to drought and bacterial pathogens simultaneously. However, information on how the drought and defence pathways interact and orchestrate global transcriptional regulation is limited. Here, we show that moderate drought stress enhances the susceptibility of Arabidopsis thaliana to Pseudomonas syringae pv. tomato DC3000. Using transcriptome meta-analysis, we found that drought and bacterial stress antagonistically modulate a large set of genes predominantly involved in salicylic acid (SA) and abscisic acid (ABA) signalling networks. We identified that the levels of SA and ABA are dynamically regulated during the course of stress. Importantly, under combined stress, drought through the ABA pathway downregulates the induction of Calmodulin-binding Protein 60 g (CBP60g) and Systemic Acquired Resistance Deficient 1 (SARD1), two transcription factors crucial for SA production upon bacterial infection. We also identified an important role of NPR1-LIKE PROTEIN 3 and 4 (NPR3/4) transcriptional repressors in the drought-mediated negative regulation of CBP60g/SARD1 expression. Using a genetic approach, we show that CBP60g/SARD1 expression is the key determinant of plant defence against bacterial pathogens under combined stress. Thus, these transcription factors act as critical nodes for the crosstalk between drought and bacterial stress signalling under combined stress in plants.

Crosstalk and trade‐offs: Plant responses to climate change‐associated abiotic and biotic stresses

“…ABA reduces the expression of two transcription factors (CBP60g and SARD1) which stimulate the production of salicylic acid (SA), an important defence hormone. This is important as droughtinduced ABA expression in Arabidopsis led to increased susceptibility to P. syringae mediated through suppression of SA-defence signalling (Mohr & Cahill, 2003Choudhary & Senthil-Kumar, 2022) ABA is also involved in the regulation of other biotic stress-related plant hormones and metabolites that can result in a trade-off for overall plant fitness. For example, drought-induced ABA signalling can downregulate Calmodulin-binding protein 60 g (CBP60g) and systemic acquired resistance deficient 1 (SARD1).…”

Emerging Roles of Salicylic Acid in Plant Saline Stress Tolerance

“…NPR1, NPR3, and NPR4 bind SA with varying affinities and play a role in binding to downstream TGA transcription factors in response to pathogen infections [ 53 ]. Moreover, the NPR3/4-mediated repression of CBP60g and SARD1 expression occurs under drought and bacterial combined stress in an SA-dependent manner, showing that NPR3/NPR4 is involved in plant resistance to abiotic stress [ 54 ]. NPR3/4 combine with TGA to inhibit downstream gene expression, whereas SA can relieve this inhibition [ 55 ].…”

CBP60‐DB: An AlphaFold‐predicted plant kingdom‐wide database of the CALMODULIN‐BINDING PROTEIN 60 protein family with a novel structural clustering algorithm

“…Because of the biological importance of CBP60g and SARD1 proteins for plant immune system resilience under changing environmental conditions (Choudhary & Senthil‐Kumar, 2022; Kim et al, 2022; Wan et al, 2012), it is critical that we fully understand their structures and functions in other plants. This mechanistic knowledge has critical ramifications on safeguarding plant disease resistance for a warming climate.…”