Study of Inflorescence Identity and Floral Determinacy Genes on Inflorescence Transition in Titanotrichum

In certain angiosperms, vegetative growth, such as leaves and asexual propagules formation on inflorescence, may reappear after floral commitment. This phenomenon is named “floral reversion”. Floral reversion is probably essential for pseudovivpary plants’ survival for its life history, i.e. sexual reproduction can be replaced by asexual propagation, such as bulbils. Titanotrichum oldhamii (Gesneriaceae), one of pseudoviviparous plant, is native in Taiwan. Its flowering inflorescence can reverse to the bulbiliferous shoot after flowering. What molecular mechanism controls the floral reversion in Titanotrichum is of particular interest. Four candidate genes including floral meristem identity gene ToFLO, inflorescence meristem identity gene ToCEN, floral organ identity gene ToPLE and shoot apical meristem stem cell identity gene ToROA were isolated in this study. Expression patterns of these genes were compared among developmental stages: before and during the inflorescence transition. Putative inflorescence meristem identity gene ToCEN is the only candidate gene whose expression was alternated when inflorescence transition occurred. During the floral differentiation, ToCEN is not expressed in the floral meristems but in meristems that are potentially transferred to the bulbiliferous shoot. It is known that overexpression of TFL1/CEN homolog in Arabidopsis and rice promotes vegetative growth and branching of inflorescence. Thus, inflorescence transition in Titanotrichum may be associated with ToCEN in obtaining vegetative meristem identity. In contrast to ToCEN, the floral meristem identity gene ToFLO could somehow be expressed in bulbiliferous meristem. This result might imply that down-regulation of ToFLO is not necessary for inflorescence transition, and ToFLO is not sufficient to provide floral differentiation as well. Thus, there is not enough evidence to support that inflorescence transition is due to loss of floral meristem identity. In conclusion, I propose the inflorescence meristem identity gene ToCEN is a good candidate for studying the inflorescence transition in Titanotricum. Further functional study would be helpful to ensure the role of ToCEN in inflorescence transition.