Stem Maturation Associated with Gravi-Response Cause Sympodial Shoot Structure in Solanaceae

Plant stems have a crucial time point to react against gravity vectors at a certain developmental stage on Earth. The sensitivity against gravity has been evolved differently among species and tissues. In Solanaceae, shoot architecture has been remarkably diversed, developing sympodial shoot (or sympodial inflorescence) carrying single flower to both sympodial shoot and inflorescence producing compound flowers. To understand this divergence, we hypothesize that sympodial growths were differently decided by maturation states and potential gravi-response of lateral meristem after floral transition of central meristem. Here we show that tomato inflorescence could be shifted to sympodial shoot growth in mutants having inflorescence meristems in the delayed maturation state molecularly. Tomato inflorescence grows to horizontal direction. However, mc sp double and s single mutant developed inflorescence growing upright direction, which is similar with the one of S. peruvianum. Erect type and inflorescences reverted to vegetative state were developed in sft, mc, and j background. Moreover, sft, j double produced only sympodial shoots carrying single flower, which is similar plant structure with sympodial shoot of N. benthamiana. Interestingly, molecular state of inflorescence meristems indicated a delay in the maturation of the meristems in s mutant and sft mutant. Therefore, we suggest that sympodial shoot meristem and sympodial inflorescence meristem might have been evolved by difference of maturation and activity of gravi-response on each young stem in Solanaceae.