Difference of Inflorescence Architecture in Solanaceae Drived By Divergent Evolution of Genes and Gene Expression Programs during Reproductive Transition

Inflorescence architecture is remarkably divergent in Solanaceae, developing a single flower to highly branched multi-flower inflorescences. The phenotypic variations might be caused by evolution of regulation of genes and proteins that lead to differential execution of conserved developmental programs. One hypothesis for is that meristem mature at different rates, affecting the final inflorescence form. To test this hypothesis and characterize the evolutionary variation in rates of maturation, we used deep sequencing to capture transcriptomes during meristem maturation from Solanaceae species representing the quantitative range of inflorescence architecture. We find that transcriptomes are more similar at both early (vegetative) and late (floral) meristem maturation stages, and genes that peak in expression in these two stages are evolutionarily more conserved than genes peak in expression at the transition stage from vegetative to reproductive phase. We also found that the transcripts of AN orthlogs, known as floral initiation marker, and S orthologs, known as inflorescence meristem marker, are diversely expressed in the transition meristems, which are a precocious expression of them in single flower species (N. benthamiana) and  a delayed expression of them in multi branched flower species (S. peruvianum). Therefore, we suggest that greater branching is associated with a pronounced delay in meristem maturation whereas production of simple inflorescence such as single flower is associated with significantly faster progression of maturation. We also propose “bubble” model for the evolution of meristem maturation, showing divergent evolution in both gene sequences and their expression patterns at reproductive transition, drives Solanaceae inflorescence architecture evolution.