SbbHLH85, a bHLH Member, Modulates Resilience to Salt Stress By Regulating Root Hair Growth in Sweet Sorghum

Abstract Introduction: bHLH family proteins play an important role in plant stress response. However, the molecular mechanism regulating salt response of bHLH is largely unknown.Materials and Methods: Here, we investigated the function and regulating mechanism of the sweet sorghum SbbHLH85 during salt stress. Results: Results show that SbbHLH85, different from its homologs in other species, is a new atypical bHLH transcription factor and is a key gene for root development in sweet sorghum. Knockout of SbbHLH85 in sorghum by CRISPR-Cas9 results in the inhibition of root development. Overexpression of SbbHLH85 resulted in significantly increased number and length of root hairs by participating in ABA and auxin signaling pathways, which can increase the absorption of Na+. While SbbHLH85 plays a negative regulatory role in salt tolerance of sorghum. Through screening yeast two-hybrid library, we identified a potential interaction partner of SbbHLH85 that is phosphate transporter chaperone PHF1, which modulates the distribution of phosphate. Both yeast two-hybrid and BiFC experiments confirmed interaction between SbbHLH85 and PHF1. Discussion: Based on these results, we suggest that the increase of Na+ content and the decrease of Pi content result in the salt sensitivity of transgenic sorghum.