Functional Conservation and Redundancy of Duplicated AGAMOUS Homologs in Regulating Floral Organ Development of Tagetes erecta

Asteraceae, as the largest angiosperm family, has an architecturally complex capitulum (inflorescences) composed of heteromorphic florets with distinct morphologies and functions. AGAMOUS (AG) MADS-box transcription factors act as key regulators in flower development and are essential for the formation of the characteristic capitulum and florets. To explore the potential functions of the AG genes in Asteraceae, we conducted a genome-wide identification and analysis of 52 AG-like genes across 22 species within this family. Additionally, we studied the functions of the Tagetes erecta class C genes TeAG1 and TeAG2 by introducing these genes into T. erecta and Nicotiana tabacum. Gene structure and phylogenomic analyses indicated that AG-like genes may have conserved and specific biological functions in Asteraceae plants. Phenotypic analyses revealed that the T. erecta class C genes TeAG1 and TeAG2 played a conserved and redundant role in regulating stamen and carpel development. The simultaneous downregulation of TeAG1 and TeAG2 led to the homeotic transformation of both stamens and carpels into corolla-like structures. However, silencing TeAG1 or TeAG2 individually in T. erecta did not affect any floral organ development. Furthermore, the ectopic expression of TeAG1 and TeAG2 in N. tabacum resulted in the transformation of sepals into pistils and corollas into stamens, respectively. Additionally, qRT-PCR analyses revealed that TeAG1 and TeAG2 repressed the expression of class A genes. Our findings expand our understanding of the function of class C genes within Asteraceae and provide strategies for breeding double-flower cultivars.