Four TFL1CEN-Like Genes on Distinct Linkage Groups Show Different Expression Patterns to Regulate Vegetative and Reproductive Development in Apple (Malusdomestica Borkh.)

Recent molecular analyses in several plant species revealed that TERMINAL FLOWER1 (TFL1) and CENTRORADIALIS (CEN) homologs are involved in regulating the flowering time andor maintaining the inflorescence meristem. In apple (Malusdomestica Borkh.), four TFL1CEN-like genes, MdTFL1, MdTFL1a, MdCENa and MdCENb, were found and mapped by a similar position on putatively homoeologous linkage groups. Apple TFL1CEN-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 -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 TFL1CEN-like genes during evolution in apple.