RcbHLH59-RcPRs module enhances salinity stress tolerance by balancing Na + /K + through callose deposition in rose ( Rosa chinensis ).

Basic helix-loop-helix (bHLH) proteins play pivotal roles in plant growth, development, and stress responses. However, the molecular and functional properties of bHLHs have not been fully characterized. In this study, a novel XI subgroup of the bHLH protein gene RcbHLH59 was isolated and identified in rose ( Rosa sp . ). This gene was induced by salinity stress in both rose leaves and roots, and functioned as a transactivator. Accordingly, silencing RcbHLH59 affected the antioxidant system, Na + /K + balance, and photosynthetic system, thereby reducing salt tolerance, while the transient overexpression of RcbHLH59 improved salinity stress tolerance. Additionally, RcbLHLH59 was found to regulate the expression of sets of pathogenesis-related ( PR ) genes in RcbHLH59 -silenced (TRV- RcbHLH59 ) and RcbHLH59 -overexpressing ( RcbHLH59- OE) rose plants. The RcPR4/1 and RcPR5/1 transcript levels showed opposite changes in the TRV- RcbHLH59 and RcbHLH59- OE lines, suggesting that these two genes are regulated by RcbHLH59 . Further analysis revealed that RcbHLH59 binds to the promoters of RcPR4/1 and RcPR5/1, and that the silencing of RcPR4/1 or RcPR5/1 led to decreased tolerance to salinity stress. Moreover, callose degradation- and deposition-related genes were impaired in RcPR4/1 - or RcPR5/1 -silenced plants, which displayed a salt tolerance phenotype by balancing the Na + /K + ratio through callose deposition. Collectively, our data highlight a new RcbLHLH59-RcPRs module that positively regulates salinity stress tolerance by balancing Na + /K + and through callose deposition in rose plants.