Recessive antimorph alleles reveal novel functions of the Opaque1 myosin XI in maize.

Ideal plant architecture optimizes canopy structure and increases grain yield in maize. However, its underlying genetic mechanisms remain poorly characterized. Two recessive, EMS-induced maize mutants were identified that have reduced stature, opaque kernels, and abnormal subsidiary cell division and are allelic to Opaque1 (o1) which encodes myosin XI-I. These 2 new missense alleles, o1-2995 and o1-tan62, unlike the loss-of-function alleles previously identified, generate O1 protein but paradoxically generate more severe morphological defects. These defects include reduced internode elongation and partial suppression of excessive tassel and ear branching in ramosa1 (ra1), ra2, and ra3 mutants. We show that o1-2995 and o1-tan62 are novel, antimorph alleles of o1 and play a role in plant growth via internode elongation, subsidiary cell division positioning, leaf patterning, inflorescence development, and overall plant architecture.