Combinatorial control of meristem identity in maize inflorescences

Nicholas J Kaplinsky,Michael Freeling

doi:10.1242/dev.00336

Abstract

The architecture of maize inflorescences, the male tassel and the female ear, is defined by a series of reiterative branching events. The inflorescence meristem initiates spikelet pair meristems. These in turn initiate spikelet meristems which finally produce the floret meristems. After initiating one meristem, the spikelet pair and spikelet meristem convert into spikelet and floret meristems, respectively. The phenotype of reversed germ orientation1 (rgo1) mutants is the production of an increased number of floret meristems by each spikelet meristem. The visible phenotypes include increased numbers of flowers in tassel and ear spikelets, disrupted rowing in the ear, fused kernels, and kernels with embryos facing the base of the ear, the opposite orientation observed in wild-type ears. rgo1 behaves as single recessive mutant. indeterminate spikelet1 (ids1) is an unlinked recessive mutant that has a similar phenotype to rgo1. Plants heterozygous for both rgo1 and ids1 exhibit nonallelic noncomplementation; these mutants fail to complement each other. Plants homozygous for both mutations have more severe phenotypes than either of the single mutants; the progression of meristem identities is retarded and sometimes even reversed. In addition, in rgo1; ids1 double mutants extra branching is observed in spikelet pair meristems, a meristem that is not affected by mutants of either gene individually. These data suggest a model for control of meristem identity and determinacy in which the progress through meristem identities is mediated by a dosage-sensitive pathway. This pathway is combinatorially controlled by at least two genes that have overlapping functions.

Highlights

Plant growth consists of reiterative developmental events that determine the morphology of the mature organism
Often, reversed and normal orientation kernels are found in the same spikelet surrounded by a shared pair of glumes. rgo1 ears contain fused kernels, each containing an embryo (Fig. 2B)
The lack of a SPM phenotype despite ids1 mRNA expression suggests redundancy with another gene or genes, and given the similarity of the rgo1 and ids1 phenotypes, we investigated whether the double mutant would display a SPM phenotype

Summary

Introduction

Plant growth consists of reiterative developmental events that determine the morphology of the mature organism. The above ground portion of the plant is elaborated from the shoot apical meristem (SAM), which produces leaves, stems and axillary meristems (together called a phytomer) in a repetitive manner (Galinat, 1959; Steeves and Sussex, 1989). The reproductive structure of plants, the inflorescence, is produced by an inflorescence meristem (IM), which is derived from the SAM and/or axillary meristems. Inflorescences exhibit a wide range of meristematic behaviors in different plants, leading to the varying reproductive morphologies seen in the plant kingdom. Inflorescences range from simple and unbranched spikes to highly branched panicles. This variability can be observed within single species (Chapman and Peat, 1992). During the domestication of corn, Zea mays, from teosinte, there has been an increase in inflorescence complexity that reflects human selection for agronomically important traits (Doebley and Stec, 1991; Galinat, 1996; Iltis, 1988)

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