A Novel Homeobox Family Gene, ScH1-33, Promotes Tillering and Enhances Cold Tolerance in Sugarcane

Tillering is a critical determinant of plant architecture and yield. While numerous genes regulating tillering have been cloned and characterized, studies on tillering-related genes in sugarcane (Saccharum spp.) still remain limited. In this study, 73 ScH1 genes belonging to Homeobox (HB) gene family in the XTT22 sugarcane genome were identified. The key tillering gene ScH1 (the OsH1 homologue in sugarcane) is non-uniformly distributed across all 22 chromosomes. GUS histochemical staining revealed that the ScH1-33 promoter is exclusively active in young shoots. ScH1-33 protein localizes to the nucleus. ScH1-33-overexpressing Arabidopsis thaliana exhibited enhanced tillering and improved cold tolerance. RNA-seq analysis was performed on A. thaliana with overexpression of ScH1-33, revealing that the plant-specific MAPK signalling pathway might mediate ScH1-dependent cold tolerance enhancement. Through yeast two-hybrid library screening, the ScTSJT1 protein was identified, and the interaction between ScH1-33 and ScTSJT1 was confirmed by both in vitro and in vivo assays. We found that co-overexpression of ScH1-33 and ScTSJT1 in A. thaliana significantly increased the number of tillers compared to ScH1-33-OE lines, indicating the additive effect of ScH1-33 and ScTSJT1 in tillering control. This study provides crucial insights into the roles of HB gene in regulating tillering and stress tolerance in sugarcane.