Possible contributions of TERMINAL FLOWER 1 to the evolution of rosette flowering in Leavenworthia (Brassicaceae)

Abstract

Summary• Leavenworthia crassa is a rosette flowering species that differs from inflorescence flowering species, such as Arabidopsis thaliana, in having elongated pedicels and shortened interfloral internodes on the main axis. Based on previous experiments, we hypothesized that changes to the L. crassa TFL1 ortholog, LcrTFL1, were important in the evolution of rosette flowering.• We isolated LcrTFL1 and introduced a genomic construct into tfl1 mutant A. thaliana plants. We also generated and analyzed EGFP-LcrTFL1 reporter-fusion lines, and LcrTFL1 ⁄ LcrLFY doubly transgenic lines.• The transgene rescued the mutant defects, but manifested gain-of-function phenotypes. However, LcrTFL1 lines differed from 35S:TFL1 lines in several regards. Defects in floral meristem identity establishment were observed, as was the production of flowers with extra petals. We also noted features that resemble rosette flowering: LcrTFL1 lines produced significantly shorter interfloral internodes and significantly longer pedicels than either wild-type or 35S:TFL1 plants.• Our data show that there are substantive differences in the regulation and ⁄ or function of TFL1 orthologs between A. thaliana and L. crassa. These may reflect changes that occurred during the evolution of rosette flowering in Leavenworthia, but, if so, our results show that additional, as-yet-unidentified genes were involved in this instance of architectural evolution.

Separate elements of the TERMINAL FLOWER 1 cis-regulatory region integrate pathways to control flowering time and shoot meristem identity

“…Interestingly, the level of sequence conservation was reduced in the TFL1 orthologue of Leavenworthia crassa, a Brassicaceae species with a different plant architecture, known as rosette flowering, where plants lack an inflorescence stem and produce solitary flowers at the axil of rosette leaves (Liu et al, 2011). Noticeably, the conserved block F was missing from the L. crassa TFL1 orthologue (Fig.…”

“…Thus, different combinations of cis-regulatory modules in different species could lead to different expression patterns of TFL1-like genes, as has been predicted to contribute to different inflorescence architectures (Prusinkiewicz et al, 2007). For instance, it is interesting that in the Arabidopsis relative L. crassa, in which changes in TFL1 have been proposed to contribute to its distinct inflorescence architecture (Liu et al, 2011), the conserved block F (region IV) is absent from the 3′ of its TFL1 gene (Fig. 1A).…”

Evolutionary transgenomics: prospects and challenges

“…Another example involves the introduction of LFY and TFL1 genes from different Brassicaceae species into A. thaliana . In all three cases involving LFY ( Yoon and Baum, 2004 ; Sliwinski et al, 2007 ) and the one case involving TFL1 ( Liu et al, 2011 ), the transgene resulted in a novel phenotype and these were shown to also occur in a wildtype background showing transdominance ( Sliwinski et al, 2006 , 2007 ; Liu et al, 2011 ). Similarly, studies of REPLUMLESS ( RPL ), a gene that promotes fruit dehiscence, showed that introducing the Arabidopsis RPL gene into Brassica is sufficient to induce Arabidopsis -like fruit dehiscence in the recipient ( Arnaud et al, 2011 ).…”

Evolution and developmental genetics of floral display—A review of progress

“…Forward genetics studies have been largely restricted to model plants or crop species (Irish & Sussex, 1990;Schultz & Haughn, 1991;Shannon & Meeks-Wagner, 1991;Weigel et al, 1992;Bradley et al, 1996). Due to lack of transformation system in non-model plants, Arabidopsis thaliana has been widely used for this purpose in non-model plant studies (Rutledge et al, 1998;Pillitteri et al, 2004;Boss et al, 2006;Liu et al, 2011Liu et al, , 2016. In contrast, reverse genetics seeks to determine the phenotypes that may arise as a result of changes in particular sequences in the coding or regulatory regions.…”

“…In tomato, the TFL1 homologue SELF‐PRUNING ( SP ) was also expressed in shoot apices and leaves from very early stages, and was thought to regulate the alternation between vegetative and reproductive cycles in sympodial meristems (Pnueli et al, ). Furthermore, TFL1 ‐like genes have also been reported to function in regulating internode elongation, pedicel elongation, and intercalary meristem activity in distantly related lineages (rice, Zhang et al, ; Populus , Mohamed et al, ; Leavenworthia crassa , Liu et al, ). In Cornus , evolutionary shifts in expression levels of these genes were found to be correlated with the “branch index” of the determinate inflorescences that varied among species from condensed heads to branched paniculate cymes (Ma et al, ).…”