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

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. The ABA-responsive transcription factor MdbHLH160 enhances apple drought tolerance by promoting MdSOD1 and MdDREB2A-like expression and undergoes MdBT2-mediated ubiquitination and degradation.

Automated summary

Drought stress is a significant environmental factor that affects crop productivity, quality, and distribution. Abscisic acid (ABA) plays a crucial role in plant responses to drought, but the exact molecular mechanisms are still unclear. In this study, researchers identified an ABA-responsive bHLH transcription factor, MdbHLH160, that promotes drought tolerance in Arabidopsis and apple. MdbHLH160 directly regulates the expression of genes involved in reactive oxygen species (ROS) scavenging and dehydration responsiveness, thereby enhancing apple's ability to tolerate drought. The protein MdbHLH160 is stabilized by ABA treatment and undergoes ubiquitination and degradation through interaction with the BTB protein MdBT2. This study provides insights into the molecular mechanisms of ABA-mediated drought tolerance and highlights the importance of MdbHLH160 in enhancing apple's ability to withstand drought.