DEFINING THE FUNCTION OF RICE FLORIGENIC PROTEINS DURING THE REPRODUCTIVE TRANSITION AND INFLORESCENCE DEVELOPMENT

Inflorescence development and its regulation are crucial for rice yield and have been extensively studied. During this process, the inflorescence meristem produces indeterminate branch meristems, followed by determinate spikelet and floret meristems. Extending the indeterminate stage results in panicles with more branches and seeds. The PEBP genes that encode for florigen-like FT-L1 and anti-florigens RCN1-4, influence this mechanism. While the antagonistic relationship between florigens Hd3a and RFT1 and anti-florigens RCN1-4 in flowering time is known, their interplay in shaping panicle architecture in rice remains to be fully clarified. Our research reveals that a double mutation of FT-L1 and RFT1 increases the number of secondary and tertiary panicle branches, resulting in a more indeterminate inflorescence, suggesting their joint role in floret meristem determination. Additionally, a triple mutant ft-l1 rcn1 rcn4 shows a more determinate phenotype, although the ft-l1 mutation prevails over rcn1 rcn4, in particular in one of the ft-l1 mutant backgrounds. The antagonistic role between these proteins has been further analyzed modulating the function of FT-L1 using the Prime Editing technique, introducing an aminoacidic conversion important for the switch of the florigenic into an anti-florigenic function. My study also highlights FT-L1’s involvement in flower fertility regulation. FT-L1 transcripts and proteins are present in flowers, particularly in pistils. Reciprocal crosses indicate that female organ problems likely cause the sterility seen in ft-l1 mutants. Morphological analyses show that ft-l1 and florigen mutations lead to flower defects such as homeotic transformations of anthers into pistils or additional female organs. RNA-Seq analysis of hd3a ft-l1 vs. hd3a mutants reveals downregulation of B, C, D, and E-class genes essential for flower organ identity, supporting the phenotypes observed. Moreover, FT-L1 exhibits mobility similar to florigen proteins Hd3a and RFT1 and localizes also near plasmodesmata, co-localizing with a protein implicated in cell-to-cell trafficking. These findings increase our understanding of FT-L1’s complex role in inflorescence development and flower fertility.