Abstract
In maize (Zea mays L.), as in other grass species, stem elongation occurs during growth and most noticeably upon the transition to flowering. Genes that reduce stem elongation have been important to reduce stem breakage, or lodging. Stem elongation has been mediated by dwarf and brachytic/brevis plant mutants that affect giberellic acid and auxin pathways, respectively. Maize brevis plant1 (bv1) mutants, first identified over 80 years ago, strongly resemble brachytic2 mutants that have shortened internodes, short internode cells, and are deficient in auxin transport. Here, we characterized two novel bv1 maize mutants. We found that an inositol polyphosphate 5-phosphatase orthologue of the rice gene dwarf50 was the molecular basis for the bv1 phenotype, implicating auxin-mediated inositol polyphosphate and/or phosphoinositide signalling in stem elongation. We suggest that auxin-mediated internode elongation involves processes that also contribute to stem gravitropism. Genes misregulated in bv1 mutants included genes important for cell wall synthesis, transmembrane transport, and cytoskeletal function. Mutant and wild-type plants were indistinguishable early in development, responded similarly to changes in light quality, had unaltered flowering times, and had normal flower development. These attributes suggest that breeding could utilize bv1 alleles to increase crop grain yields.
Highlights
In grasses including Zea mays, plant height at maturity largely results from stem elongation (Moore et al, 1991)
We found that an inositol polyphosphate 5-phosphatase orthologue of the rice gene dwarf50 was the molecular basis for the bv1 phenotype, implicating auxin-mediated inositol polyphosphate and/or phosphoinositide signalling in stem elongation
We identified two reduced-height maize mutants termed 1301 and 1302 in two families segregating for ethyl methanesulphonate (EMS)-induced mutations
Summary
In grasses including Zea mays, plant height at maturity largely results from stem elongation (Moore et al, 1991). This elongation occurs primarily after the shoot apical meristem initiates the production of reproductive tissues in response to developmental and environmental signals (Siemer et al, 1969; Colasanti and Muzynski, 2009). New leaves emerge from the pseudostem, a whorl composed of the leaf sheaths of younger leaves. When eight leaf tips have emerged from the maize whorl, the shoot meristem can be below ground. Cell division and cell expansion within the internodes extend the shoot apex through the whorl.
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