Structural diversity and stress regulation of the plant immunity-associated CALMODULIN-BINDING PROTEIN 60 (CBP60) family of transcription factors inSolanum lycopersicum(tomato)

Abstract

Cellular signalling generates calcium (Ca2+) ions, which are ubiquitous secondary messengers decoded by calcium-dependent protein kinases, calcineurins, calreticulin, calmodulins (CAMs) and CAM-binding proteins. Previous studies in the model plant Arabidopsis thaliana have shown the critical roles of the CAM-BINDING PROTEIN 60 (CBP60) protein family in plant growth, stress responses and immunity. Certain CBP60 factors can regulate plant immune responses, like pattern-triggered immunity, effector-triggered immunity, and synthesis of major plant immune-activating metabolites salicylic acid (SA) and N-hydroxypipecolic acid (NHP). Although homologous CBP60 sequences have been identified in the plant kingdom, their function and regulation in most species remain unclear. In this paper, we specifically characterized 11 members of the CBP60 family in the agriculturally important crop tomato (Solanum lycopersicum). Protein sequence analyses revealed that three CBP60 homologs have the closest amino acid identity to Arabidopsis CBP60g and SARD1, master transcription factors involved in plant immunity. Strikingly, AlphaFold deep learning-assisted prediction of protein structures highlighted close structural similarity between these tomato and Arabidopsis CBP60 homologs. Conserved domain analyses revealed that they possess CAM-binding domains and DNA-binding domains, reflecting their potential involvement in linking Ca2+ signalling and transcriptional regulation in tomato plants. In terms of their gene expression profiles under biotic (Pseudomonas syringae pv. tomato DC3000 pathogen infection) and/or abiotic stress (warming temperatures), five tomato CBP60 genes were pathogen-responsive and temperature-sensitive, reminiscent of Arabidopsis CBP60g and SARD1. Overall, we present a genome-wide identification of the CBP60 gene/protein family in tomato plants, and we provide evidence on their regulation and potential function as Ca2+-sensing transcriptional regulators.

Warm temperature suppresses plant systemic acquired resistance by intercepting theN-hydroxypipecolic acid immune pathway

“…Seeds were sown into pots containing autoclaved soil mix – one-part Promix-PGX soil (Plant Products, Ancaster, Ontario), one-part Turface (Turface Athletics, Buffalo Grove, IL), and one-part Vermiculite Prolite (Therm-O-Rock, New Eagle, PA) – supplemented with 100mL of Miracle-Gro solution (The Scotts Company, Mississauga, ON). Tomato ( Solanum lycopersicum ) cultivar Castlemart plants were grown as described previously (Shivnauth et al, 2023). Rapeseed ( Brassica napus ) cultivar Westar plants were grown as described previously (Kim et al, 2022).…”

“…The resulting qPCR mixes were run using the Applied Biosystems QuantStudio3 platform (Life Technologies) or CFX96 Real-Time PCR Detection System (Bio-Rad, USA). The individual Ct values were determined for target genes and the internal control gene: PP2AA3 for Arabidopsis; SlACT2 for tomato and BnaGDI1 for rapeseed (Huot et al, 2017; Kim et al, 2022; Shivnauth et al, 2023). Gene expression values were reported as 2 −ΔCt , where ΔCt is Ct target gene –Ct internal control gene .…”