Inflorescence branching architecture is complex and diverse in the grass family. Previous models of grass branching posited multiple distinct meristem identities that differed primarily in their levels of determinacy. We have been exploring a distinct class of maize tassel sheath (tsh) mutants that fail to suppress bract growth. After examining genetic interactions in combination with transcript profiling it is now apparent that tsh mutants regulate meristem determinacy non-autonomously from the suppressed bract which acts as a novel signaling center limited to the grass family. In particular, genes regulating the blade sheath boundary (liguless2) and meristem leaf boundary (HANABA TARANU ortholog tsh1) appear to have been integrated into a network localized to the suppressed bract where they signal to the adjacent meristem and suppress bract growth as an indirect result of their boundary gene activity. The emerging model of grass inflorescence branching architecture includes multiple interacting signaling centers that influence meristem determinacy from a distance inconsistent with a simple homeotic model of meristem identity.
Dr. Clinton Whipple is an associate professor of biology at Brigham Young University. His lab investigates genetic mechanisms regulating plant development and morphological evolution.