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Plant basic helix-loop-helix (bHLH) transcription factors (TFs) play central roles in various abiotic stresses. However, its role in plant cold resistance is largely unknown. Previously, we characterised CaNAC035 in pepper, which positively regulates tolerance to cold, salt and drought stresses tolerance. Here, we identified CabHLH035, a CaNAC035-interacting protein in pepper. To explore its functions in cold stress tolerance, we silenced the gene in pepper via virus-induced gene silencing (VIGS) and overexpressed the gene in Arabidopsis. The results showed that CabHLH035 expression was induced by cold treatment, and silencing of CabHLH035 decreased cold stress tolerance. Conversely, overexpression of CabHLH035 in Arabidopsis increased cold stress tolerance. To investigate homologs genes of C-repeat binding factor (CBF) pathway proteins and reactive oxygen species (ROS) marker gene expression blocking by CabHLH035, we performed yeast one-hybrid (Y1H), dual luciferase and electrophoretic mobility shift assay experiments. The results showed that CabHLH035 bound to the region upstream of the CaCBF1A and CaAPX promoters. Additionally, CaCBF1A bound to the CaDHN4 promoter. Taken together, our results showed that CabHLH035 plays a crucial role in cold stress tolerance and its potential as a target for breeding cold-resistant crops. The findings provide a basis for studying the functions and regulatory network of cold stress tolerance in pepper.

Abstract The ribosomal protein contains complex structures that belong to polypeptide glycoprotein family, which are involved in plant growth and responses to various stresses. In this study, we found that capsicum annuum 40S ribosomal protein SA-like (CaSLP) was extensively accumulated in the cell nucleus and cell membrane, and the expression level of CaSLP was up-regulated by Salicylic acid (SA) and drought treatment. Significantly fewer peppers plants could withstand drought stress after CaSLP gene knockout. The transient expression of CaSLP leads to drought tolerance in pepper, and Arabidopsis’s ability to withstand drought stress was greatly improved by overexpressing the CaSLP gene. Exogenous application of SA during spraying season enhanced drought tolerance. CaSLP-knockdown pepper plants demonstrated a decreased resistance of Pseudomonas syringae PV.tomato (Pst) DC3000 (Pst.DC3000), whereas ectopic expression of CaSLP increased the Pst.DC3000 stress resistance in Arabidopsis. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) results showed that CaNAC035 physically interacts with CaSLP in the cell nucleus. CaNAC035 was identified as an upstream partner of the CaPR1 promoter and activated transcription. Collectively the findings demonstrated that CaSLP plays an essential role in the regulation of drought and Pst.DC3000 stress resistance. Graphical Abstract