Identification of key flowering-related genes and their seasonal expression in Populus tomentosa reproductive buds suggests dual roles in floral development and dormancy

Abstract

Populus is a major industrial tree species used for bioenergy, timber and pulp manufacturing, which requires an appropriate growth regulation mechanism for long-term survival in response to seasonal climatic changes. As two key processes during life cycle both controlled by photoperiod and temperature, flowering and dormancy have been suggested to share a common regulatory mechanism. In the present study, 31 flowering-related genes in several floral pathways in P. tomentosa were identified. The expression level of these genes was determined using reverse transcription quantitative real-time polymerase chain reaction in female and male buds during the eight stages across the flower bud development. Seasonal expression profiles indicated that 31 flowering-related genes showed different and specific expression trends individually during floral development and dormancy transition. Among these genes, the expression trends for the majority were different between sexes, and the expression abundance of some genes exhibited sex differences. Furthermore, co-expression networks were constructed using 31 flowering-related genes in female and male flower buds, respectively. Many modules of co-expressed genes and hub genes were identified, such as FRIGIDA in female and APETALA1 in male. The results suggested these flowering-related genes play potential dual roles both in floral development and dormancy. This is the first investigation of the expression patterns of flowering-related genes during dormancy transition in P. tomentosa reproductive buds at molecular level. This work would provide important insights to explore connections between floral development and dormancy in perennial trees, and make it possible to enhance vegetative growth and further increase woody biomass accumulation in poplar by regulating key candidate genes using biotechnology.