LEAFY and the evolution of rosette flowering in violet cress (Jonopsidium acaule, Brassicaceae)

Arabidopsis and most other Brassicaceae produce an elongated inflorescence of mainly ebracteate flowers. However, the early-flowering species violet cress (Jonopsidium acaule) and a handful of other species produce flowers singly in the axils of rosette leaves. In Arabidopsis the gene LEAFY (LFY) is implicated in both the determination of flower meristem identity and in the suppression of leaves (bracts) that would otherwise subtend the flowers. In this study we examined the role of LFY homologs in the evolution of rosette flowering in violet cress. We cloned two LFY homologs, vcLFY1 and vcLFY2, from violet cress. Their exon sequences show ～90% nucleotide similarity with Arabidopsis LFY and 99% similarity to each other. We used in situ hybridization to study vcLFY expression in violet cress. The patterns were very similar to LFY in Arabidopsis except for stronger expression in the shoot apical meristem outside of the region of flower meristem initiation. It is possible that the relatively diffuse expression of vcLFY contributes to the lack of bract suppression in violet cress. Additionally, the earliest flowers produced by violet cress express vcLFY, suggesting that accelerated flowering in violet cress could also result from changes in the regulation of vcLFY.