Heading Chinese cabbage (Brassica rapa L. syn. B. campestris L. ssp. chinensis Makino var. pekinensis (Rupr.) J. Cao et Sh. Cao) is a cruciferous Brassica vegetable that has a triplicate genome, owing to an ancient genome duplication event. It is unclear whether the duplicated homologs have conserved or diversified functions. Hydrogen sulfide (H₂S) is a plant gasotransmitter that plays important physiological roles in growth, development, and responses to environmental stresses. The modification of cysteines through S-sulfhydration is an important mechanism of H₂S, which regulates protein functions. H₂S promotes flowering in Arabidopsis and heading Chinese cabbage. Here we investigated the molecular mechanisms of H₂S used to promote flowering in the latter. Four, five, and four BraFLC, BraSOC I, and BraFT homologs were identified in heading Chinese cabbage. Different BraFLC proteins were bound to different CArG boxes in the promoter regions of the BraSOC I and BraFT homologs, producing different binding patterns. Thus, there may be functionally diverse BraFLC homologs in heading Chinese cabbage. Exogenous H₂S at 100 μmol L^-1 significantly promoted flowering by compensating for insufficient vernalization. BraFLC 1 and BraFLC 3 underwent S-sulfhydration by H₂S, after which their abilities to bind most BraSOC I or BraFT promoter probes weakened or even disappeared. These changes in binding ability were consistent with the expression pattern of the BraFT and BraSOC I homologs in seedlings treated with H₂S. These results indicated that H₂S signaling regulates flowering time. In summary, H₂S signaling promoted plant flowering by weakening or eliminating the binding abilities of BraFLCs to downstream promoters through S-sulfhydration.

Zhuoya Pei

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