NtAGL6 of Narcissus tazetta var. chinensis Promotes Flowering via an Indirect Activation Pathway of FT.

Narcissus tazetta var. chinensis is a monocot with unique floral morphology and heat-induced flowering. In Arabidopsis, the MADS-box gene AGL6 promotes flowering by positively regulating FT expression, but whether this regulatory mechanism is conserved in monocots remains unknown. Here, we cloned the AGL6 homolog NtAGL6 from N. tazetta var. chinensis, analyzed its sequence, phylogeny, expression pattern, and promoter cis-elements, and performed ectopic expression in wild-type and ap1 mutant Arabidopsis. Yeast one-hybrid and transient expression assays were used to test its interaction with the NtFT1 promoter. NtAGL6 was specifically expressed in floral organs and during flower bud differentiation, and its promoter contained heat shock and gibberellin response elements. Ectopic expression of NtAGL6 promoted flowering in Arabidopsis and upregulated FT, SOC1, LFY, and AP1, and partially rescued petal and sepal defects in the ap1 mutant. Although NtAGL6 activated NtFT1 promoter activity in transient assays, yeast one-hybrid assays detected no direct binding. Together, these results indicate that NtAGL6 promotes flowering and affects A-class floral organ identity, but likely regulates FT through an indirect pathway in this monocot. This study provides new insights into the functional divergence of AGL6 in flowering regulation in monocots.