Tassels replace upper ears1 encodes a putative transcription factor that regulates maize shoot architecture by multiple pathways

Abstract

Plant shoot architecture has many features including inflorescence sex, branching and internode elongation, which is largely controlled by the activities of shoot apical meristem (SAM) and axillary meristems (AxM). The pleiotropic maize mutant tassels replace upper ears1 (tru1) shows reduced apical dominance with elongated upper shanks tipped by lateral tassels and shortened upper stem, altered tassel phenotypes with shortened tassel length and branch length, and reduced tassel branch number. To investigate the effect of tru1 on shoot architecture, morphological analysis of tru1-ws mutant was performed, including treatments of supplemental gibberellic acid (GA3), far red (FR) light and decapitation, and genetic interaction tests with ramosa1 (ra1), tasselseed1 (ts1), teosinte branched1 (tb1), barren inflorescence2 (bif2), barren stalk1 (ba1), and Dwarf8 (D8) mutants. Here, we first report the novel functions of ts1 in tru1-mediated inflorescence branching pathway. We found that tru1 acts as a positive growth regulator to promote elongation of internodes in the upper main stem (1° axis) and in the tassel, and branching in the tassel, but acts as a negative growth regulator to inhibit elongation of internodes in the shank (2° axis) and the ear, and determination of male inflorescence sex. Therefore, tru1 functions as an integrator of multiple pathways including inflorescence sex and branching, inflorescence and internode elongation in regulation of maize shoot architecture.