Low temperature downregulates MabHLH355 and its associated target genes responsible for scavenging ROS in banana peel under cold stress

Basic helix-loop-helix (bHLH) transcription factors are involved in mediating plant responses to environmental stresses. However, its role in the stress response in banana is largely unknown. In this manuscript, a comprehensive analysis was conducted to reveal the involvement of MabHLHs and their significance in banana cold stress responses. A total of 366 putative MabHLH transcription factors were identified. These MabHLHs were named according to their chromosomal locations and grouped into 12 subfamilies, with segmental duplication events significantly contributing to the expansion of this family. Transcriptomic analysis based on WGCNA identified 37 MabHLHs in co-expression networks under cold stress conditions. Among these MabHLHs, MabHLH355 in the magenta module, belonging to the IIIe subfamily, was downregulated under cold stress and significantly correlated with phenotypic indices, including H2O2, MDA and O2•- content. Dual-luciferase transient expression analysis and electrophoretic mobility shift assays showed that MabHLH355 activated the expression of MaGSTF12 and MaGSTT1. Notably, transient overexpression of MabHLH355 in banana fruit improved cold tolerance. In conclusion, low temperatures repressed the expression of MabHLH355, which decreased the expression of MaGSTF12 and MaGSTT1, thereby contributing to the occurrence of chilling injuries in banana.