Analysis of Homologs of Meristem Identity Genes LEAFY and TERMINAL FLOWER 1 in the Genus Leavenworthia .

摘要

The genus Leavenworthia, in contrast to almost all Brassicaceae, has a primary inflorescence axis that does not elongate. This study attempts to shed light on the genetic changes that resulted in the evolution of a compressed primary inflorescence in Leavenworthia. Previously, transgenic experiments that introduced homologs of LEAFY (LFY) and Terminal Flower 1 (TFL1) from L. crassa into Arabidopsis thaliana suggested that both could have contributed to the origin of a compressed primary axis with long pedicels, although the data suggested that additional genes were likely also involved. The Leavenworthia phylogeny constructed using Maximum Likelihood (ML) and Bayesian methods was consistent with the results from earlier studies and suggested existence of duplicate copies of both LFY and TFL1 (here named Copy-A and Copy-B). It was also found that TFL1-A copy, which had not previously been discovered, has an intact 3' regulatory region that included two putative APETALA1 (AP1) binding sites and one putative LFY binding site, which contrasts with the B copy, which has lost the LFY binding site and two of the three AP1 binding sites. The study then brings molecular evolutionary analysis to bear, testing the hypothesis that gene duplication and/or positive selection acting on the LFY and TFL1 loci contributed to the derived phenotype of Leavenworthia. Molecular evolutionary analysis, suggested a deficit of non-synonymous substitutions in both LFY and TFL1, consistent with ongoing purifying selection acting on both copies. There was no evidence of positive selection or evidence that the A and B copies have been subject to different modes of selection. RT-PCR analysis was used to compare the expression of the A and B copies of LFY and TFL1. In both cases, the paralogs showed different expression patterns, raising the possibility that changes in gene regulation following gene duplication could have contributed to the evolution of the compressed primary inflorescence phenotype of Leavenworthia. The findings in this study could form the basis of a whole new set of research areas in the genus Leavenworthia including but not restricted to systematics, cytology, transcriptomics and gene network analysis.