Members of the bHLH family of transcription factors play important roles in multiple aspects of plant biological processes, for instance, abiotic stress responses. Previously, we characterized CaNAC035 a gene that positively regulates stress tolerance and identified CabHLH035, a CaNAC035-interacting protein in pepper (Capsicum annuum L.). In this study, we describe the role of CabHLH035 in the response to salt stress. Our results show that the expression of CabHLH035 increased following salt treatment. Transient expression of CabHLH035 (CabHLH035-To) in pepper enhanced salt tolerance, ectopic expression of CabHLH035 in Arabidopsis increased the salt stress tolerance, whereas knocking down the expression of CabHLH035 in pepper plants resulted in decreased salt tolerance. Homologs of the Salt Overly Sensitive 1 (SOS1) and pyrroline-5-carboxylate acid synthetase (P5CS) genes showed drastically increased expression in transgenic Arabidopsis plants expressing CabHLH035 and CabHLH035-To plants, but expression decreased in CabHLH035-silenced plants. Our results also showed that CabHLH035 can directly bind to the CaSOS1 and CaP5CS gene promoters and positively activate their expression. We found that transgenic Arabidopsis plants, ectopic expression of CabHLH035 and pepper plants transiently overexpressing CabHLH035 (CabHLH035-To) showed lower Na+ and higher proline contents in response to NaCl treatment, while CabHLH035-silenced plants had higher Na+ and lower proline concentrations. Overall, CabHLH035 plays important roles in salt tolerance through its effects on the intracellular Na+: K+ ratio and proline biosynthesis.
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
The ribosomal protein SA plays an essential role in multiple aspects and is involved in plant growth and response to various stresses. Drought threatens pepper yield and quality. However, the resistance mechanism of pepper in response to drought are complex and not yet fully understood. Here, we describe the role of CaSLP in mediating pepper tolerance to drought stress. we found that CaSLP was highly expressed under drought and salicylic acid (SA) stress, and CaSLP was localized in cell nucleus and cytomembrane. Knockout of CaSLP gene significantly decreased the pepper drought tolerance, while transient expression of CaSLP leads to drought tolerance in pepper, and overexpression of the CaSLP dramatically increased the drought stress tolerance in Arabidopsis. Furthermore, exogenous spring salicylic acid enhanced drought tolerance. The characterization of resistance molecular mechanisms in the Pseudomonas syringae pv. Tomato DC3000 (Pst.DC3000) is of great significance for the pepper yield and quality, we found that CaSLP-knockdown pepper plants demonstrated decreased Pst.DC3000 tolerance, whereas ectopic expression of the CaSLP increased the Pst.DC3000 stress tolerance in Arabidopsis. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) results showed that CaNAC035 physically interacts with CaSLP in the cell nucleus, and the CaNAC035 was identified as an upstream partner of the CaPR1 promoter and activated the transcription. Taken together, our data demonstrated that CaSLP plays an essential role in the regulation of drought stress. Our study elucidates the roles of CaSLP response to drought stress tolerance. Furthermore, a possible regulatory model and molecular mechanisms under drought stress is proposed.
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