The roles and evolution of the four LEAFY homologues in floral patterning and leaf development in woodland strawberry

Abstract

The plant-specific transcription factor LEAFY (LFY), generally maintained as a single copy gene in most angiosperm species, plays critical roles in flower and leaf development. However, wild strawberry Fragaria vesca possesses four LFY homologues in the genome, their respective functions and evolution remain unknown. Through chemical mutagenesis screen, we identified two allelic mutations in one of the four LFY homologues, FveLFYa, in F. vesca, causing homeotic conversion of floral organs and reiterative outgrowth of ectopic florets. Both CRISPR-knockout and transgenic rescue confirmed the identity of FveLFYa. Ectopic expression in Arabidopsis lfy-5 mutant revealed that only FveLFYa and FveLFYb can rescue the flower defects and induce solitary flowers in leaf axils. Disruption of FveLFYc, the second abundantly expressed LFY homologue, caused no obvious morphology phenotypes in F. vesca. FveLFYb and FveLFYd are barely expressed. Expression of FveAP1, homologue of the well-known LFY target AtAP1, is not changed in the fvelfya flowers, possibly caused by an absence of any FveLFYa binding site in its promoter. Loss of Axillary Meristems encodes a GRAS transcription factor essential for stamen initiation. The ectopic florets are eliminated in fvelfya lam, suggesting that LAM is required for floret production. Moreover, approximately 30% of mature leaves have smaller or fewer leaflets in fvelfya. Among these homologues, only FveLFYa is syntenic to the homologues in other species. Overall, the detailed analyses of the four LFY homologues in woodland strawberry demonstrate that only FveLFYa plays crucial roles in floral patterning with rewired gene network.