TaSGT1 increased salt stress tolerance through the TaSGT1-TaRGLG2-TaPPCa model in wheat

High salt in the soil limits plant growth and crop productivity. Under salt stress, plants have evolved various adaptive mechanisms, among which protein degradation by ubiquitination is an effective one. SGT1 is an inhibitory factor of the S-phase kinase-associated protein 1 (Skp1) G2 allele. It is well known that SGT1 is a key regulator of R-gene-mediated disease resistance. But little is known about its function and molecular mechanism in regulating salt stress tolerance. In this study, using yeast two-hybridization analysis, we identified an SGT1 in wheat. It was induced for expression by NaCl and exogenous abscisic acid (ABA) treatment. The fluorescence signal of TaSGT1-GFP fusion protein was located on the endoplasmic reticulum membrane. TaSGT1B overexpressing transgenic wheat exhibited more well-developed roots and earlier flowering but had a lower plant height compared to the wild-type plants. Also, overexpression of TaSGT1B increased salt, PEG, and drought stress tolerance as well as ABA sensitivity in wheat. While the TaSGT1 edited wheat lines showed opposite phenotypes. Interaction analysis demonstrated TaSGT1 directly interacted with the ubiquitin ligase TaRGLG2. Further, TaRGLG2 interacted with TaPP2Ca (5, 7, 8, 9) and could mediate their ubiquitination. The activity of TaPP2Ca was lower in TaSGT1B overexpressing transgenic wheat than in the wild-type line under salt stress. All these results demonstrated that TaSGT1 mediated the ubiquitin-mediated degradation of the negative regulatory factor TaPP2Ca through a TaSGT1-TaRGLG2-TaPP2Ca model, thereby enhancing salt stress tolerance.