Endogenous H2S promotes Arabidopsis flowering through the regulation of GA20ox4 in the gibberellin pathway.

Flowering time is a critical determinant of plant reproductive success and agricultural yield. Hydrogen sulfide (H₂S), as a signaling molecule, regulates various aspects of plant growth and development. In this study, we examined the role of endogenous H₂S in regulating flowering time in Arabidopsis. The O-acetylserine thiol lyase a1 (oasa1) mutant, which has elevated H₂S levels due to impaired OASA1 activity that catalyzes the synthesis of Cys from H2S, flowers earlier than wild type (WT). The OASA1 overexpression lines (OE-OASA1-#33/#142), characterized by reduced H₂S levels, show delayed flowering, accompanied by decreased expression of key flowering regulators, FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), and AGAMOUS-LIKE24 (AGL24). Notably, vernalization and short-day (SD) conditions did not affect their flowering patterns. Exogenous H₂S and GA₃ treatment rescued the delayed flowering phenotype of OE-OASA1-#33/#142. In oasa1, levels of GA intermediates (GA15 and GA53) were elevated, while their levels were reduced in OE-OASA1-#33/#142. RT-qPCR analysis showed a significant reduction in the expression of GIBBERELLIN 20-OXIDASE 4 (GA20ox4) in OE-OASA1-#33/#142 compared to WT. Overexpression of GA20ox4 (OE-GA20ox4-#20/#30) resulted in earlier flowering and partially rescued the delayed flowering phenotype of OE-OASA1-#33/#142. Additionally, the expression of age pathway-related genes, including miRNA172b and SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 3/4/5/9/15 (SPL3/4/5/9/15), was significantly reduced in OE-OASA1-#33/#142 seedlings. These findings suggest that endogenous H₂S positively regulates GA20ox4 expression, thereby promoting gibberellin synthesis and advancing flowering in Arabidopsis through the GA pathway. Furthermore, the promotion of flowering by H₂S appears to be linked to the age pathway.