Four TFL1/CEN-Like Genes on Distinct Linkage Groups Show Different Expression Patterns to Regulate Vegetative and Reproductive Development in Apple (Malus×domestica Borkh.)

Abstract

Recent molecular analyses in several plant species revealed that TERMINAL FLOWER1 (TFL1) and CENTRORADIALIS (CEN) homologs are involved in regulating the flowering time and/or maintaining the inflorescence meristem. In apple (Malusxdomestica Borkh.), four TFL1/CEN-like genes, MdTFL1, MdTFL1a, MdCENa and MdCENb, were found and mapped by a similar position on putatively homoeologous linkage groups. Apple TFL1/CEN-like genes functioned equivalently to TFL1 when expressed constitutively in transgenic Arabidopsis plants, suggesting that they have a potential to complement the TFL1 function. Because MdTFL1 and MdTFL1a were expressed in the vegetative tissues in both the adult and juvenile phases, they could function redundantly as a flowering repressor and a regulator of vegetative meristem identity. On the other hand, MdCENa was mainly expressed in fruit receptacles, cultured tissues and roots, suggesting that it is involved in the development of proliferating tissues but not in the control of the transition from the juvenile to the adult phase. In contrast, MdCENb was silenced in most organs probably due to gene duplication by the polyploid origin of apple. The expression patterns of MdTFL1 and MdCENa in apple were also supported by the heterologous expression of beta-glucuronidase fused with their promoter regions in transgenic Arabidopsis. Our results suggest that functional divergence of the roles in the regulation of vegetative meristem identity may have occurred among four TFL1/CEN-like genes during evolution in apple.

Contributions of Flowering Time Genes to Sunflower Domestication and Improvement

“…Thus, our findings challenge the prediction that downstream genes like FT are more likely to exhibit regulatory variation (Schwartz et al 2009). The redundancy afforded by a recent history of duplication, the novel derived expression domain of HaFT1, or multifarious selection acting on multiple pleiotropic effects may have uniquely fostered a selective sweep on a structural change in this case (Blackman et al 2010); however, given the expansion of FT/TFL1 homolog numbers observed in other species (Carmel-Goren et al 2003;Faure et al 2007;Nishikawa et al 2007;Danilevskaya et al 2008;Igasaki et al 2008;Mimida et al 2009), similar results may soon be observed in additional systems. FIGURE S1.-Sunflower COL homologs cluster with the CO-COL1-COL2 clade.…”

“…The other gene, c2588, belongs to the same gene family as INDETERMINATE1/EARLY HEADING DATE2 (ID1/Ehd2), a zinc-finger transcription factor and upstream regulator of FT homologs in monocots (Colasanti et al 1998;Matsubara et al 2008). While TFL1 homologs regulate flowering and other photoperiodic responses across diverse plants (Bradley et al 1997;Pnueli et al 1998;Nakagawa et al 2002;Foucher et al 2003;Guo et al 2006;Danilevskaya et al 2008;Ruonala et al 2008;Mimida et al 2009), the function of ID1/Ehd2 homologs in flowering may be monocot-specific. No direct ID1/Ehd2 ortholog exists in the A. thaliana genome, and phylogenetic analyses indicate the INDETERMINATE gene family independently diversified in the monocot and eudicot lineages (Colasanti et al 2006).…”

Overexpression of Arabidopsis FT gene in apple leads to perpetual flowering

“…Members of the Rosaceae family have conserved orthologs of TFL1 (Chen et al 2013;Iwata et al 2012;Mimida et al 2012), which are functionally similar to TFL1. A TFL1-like gene family is found in apple (Kotoda and Wada 2005;Mimida et al 2009Mimida et al , 2012, which might function redundantly as a flowering repressor and regulator of vegetative growth. Suppression of MdTFL1 expression by antisense oligomers or gene silencing results in induction of precocious flowering in transgenic apples (Flachowsky et al 2012;Kotoda et al 2006) and simultaneously reduces vegetative growth.…”

Tracing a key player in the regulation of plant architecture: the columnar growth habit of apple trees (Malus × domestica)

“…Buds are highly important for both vegetative and reproductive growth of trees since they are in fact undeveloped shoots. While most trees produce vegetative buds that develop into vegetative shoots and flower buds that develop into flowers, some species such as apple and pear produce vegetative and mixed buds, the latter of which can develop into leafy shoots as well as flowers (Mimida et al 2009). In these species, a mixed unit (''bourse'') containing vegetative and floral organs can occur.…”