Diversity of the woodland strawberry inflorescences results from heterochrony antagonistically regulated by FvTFL1 and FvFT1

Abstract

A vast variety of inflorescence architectures have formed during angiosperm evolution. Here we analyze the diversity and development of the woodland strawberry inflorescence. We show that it is a thyrse: a compound inflorescence in which the primary monopodial axis supports lateral sympodial branches, thus combining features of racemes and cymes. We demonstrate that this architecture is related to differences in the size and shape of the primary and lateral inflorescence meristems. We further show that woodland strawberry homologs of TERMINAL FLOWER 1 (TFL1) and FLOWERING LOCUS T (FT) antagonistically regulate the development of both the racemose and cymose components of the strawberry thyrse: the loss of functional FvTFL1 and overexpression of FvFT1 reduce the number and complexity of the cymose components, whereas silencing of FvFT1 has the opposite effect and can partially rescue the fvtfl1 mutation. We complement our experimental findings with a computational model, which captures the development of the woodland strawberry inflorescence using a small set of rules, and shows that its phenotypic diversity can be explained in terms of heterochrony resulting from the opposite action of FvTFL1 and FvFT1 on the progression from the branching to flowering state.