MdbHLH160 is stabilized via reduced MdBT2-mediated degradation to promote MdSOD1 and MdDREB2A-like expression for apple drought tolerance

Abstract

Drought stress is a key environmental factor limiting the productivity, quality, and geographic distribution of crops worldwide. Abscisic acid (ABA) plays an important role in plant drought stress responses, but the molecular mechanisms remain unclear. Here, we report an ABA-responsive bHLH transcription factor, MdbHLH160, which promotes drought tolerance in Arabidopsis (Arabidopsis thaliana) and apple (Malus domestica). Under drought conditions, MdbHLH160 is directly bound to the MdSOD1 (superoxide dismutase 1) promoter and activated its transcription, thereby triggering reactive oxygen species (ROS) scavenging and enhancing apple drought tolerance. MdbHLH160 also promoted MdSOD1 enzyme activity and accumulation in the nucleus through direct protein interactions, thus inhibiting excessive nuclear ROS levels. Moreover, MdbHLH160 directly upregulated the expression of MdDREB2A-like, a DREB (dehydration-responsive element binding factor) family gene that promotes apple drought tolerance. Protein degradation and ubiquitination assays showed that drought and ABA treatment stabilized MdbHLH160. The BTB protein MdBT2 was identified as an MdbHLH160-interacting protein that promoted MdbHLH160 ubiquitination and degradation, and ABA treatment substantially inhibited this process. Overall, our findings provide insights into the molecular mechanisms of ABA-modulated drought tolerance at both the transcriptional and post-translational levels via the ABA–MdBT2–MdbHLH160–MdSOD1/MdDREB2A-like cascade.

Joint transcriptomic and metabolomic analysis provides new insights into drought resistance in watermelon (Citrullus lanatus)

“…Overexpression of SlbHLH96 in tomato improves drought resistance by stimulating the expression of genes encoding antioxidants, ABA signaling molecules, and stress-related proteins (Liang et al, 2022). Under drought, ABA signaling activates MdbHLH160-mediated expression of MdSOD1 and MdDREB2A-like by promoting the stability of the MdbHLH160 protein, thereby positively regulating apple drought tolerance (Mao et al, 2024). The overexpression of IbbHLH118 in potatoes reduced plant tolerance to drought stress, while the overexpression IbbHLH66 improved plant tolerance to drought stress.…”

Functions of Basic Helix–Loop–Helix (bHLH) Proteins in the Regulation of Plant Responses to Cold, Drought, Salt, and Iron Deficiency: A Comprehensive Review

“…103 Of note, MdbHLH160 directly activates and binds to the E-box in the promoters of MdDREB2A-like and MdSOD1 that positively modulate drought tolerance in apples. 221 Another research group discovered that CgbHLH001 directly interacts with CALCIUM-DEPENDENT PROTEIN KINASE (CgCDPK) from Chenopodium glaucum, at the plasma membrane. 222 Ample evidence demonstrates that bHLH TFs function as binary or ternary complexes to regulate the expression of target genes during drought stress (Figure 4C).…”

“…Among them, MdbHLH93 binds directly to the E-box in the MdTyDC promoter and activates its expression, which enhances drought tolerance . Of note, MdbHLH160 directly activates and binds to the E-box in the promoters of MdDREB2A-like and MdSOD1 that positively modulate drought tolerance in apples . Another research group discovered that CgbHLH001 directly interacts with CALCIUM-DEPENDENT PROTEIN KINASE (CgCDPK) from Chenopodium glaucum , at the plasma membrane …”