ABSTRACT
A better understanding of spike development can contribute to improving wheat productivity. MADS-box genes VRN1 and FUL2 (SQUAMOSA-clade) play critical and redundant roles in wheat spike and spikelet development, where they act as repressors of MADS-box genes of the SHORT VEGETATIVE PHASE (SVP) clade (VRT2, SVP1 and SVP3). Here, we show that wheat vrt2 svp1 mutants are late flowering, have shorter stems, increased number of spikelets per spike and unusual axillary inflorescences in nodes of the elongating stem. Constitutive expression of VRT2 resulted in leafy glumes and lemmas, reversion of basal spikelets to spikes, and down-regulation of MADS-genes involved in floral development. Moreover, constitutive expression of VRT2 enhanced spikelet defects of ful2, whereas vrt2 reduced vegetative characteristics in the spikelets of vrn1 ful2 mutants heterozygous for VRN-A1. These SVP-SQUAMOSA genetic interactions were paralleled by physical interactions among their encoded proteins. SVP proteins were able to reduce SQUAMOSA-SEPALLATA interactions in yeast-three-hybrid experiments. We propose that SQUAMOSA-SVP complexes act during the early reproductive phase to promote heading, formation of the terminal spikelet, and stem elongation, but that down-regulation of SVP genes is then necessary for the formation of SQUAMOSA-SEPALLATA complexes that are required for normal spikelet and floral development.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
The author(s) responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) are: Jorge Dubcovsky (jdubcovsky{at}ucdavis.edu) and Juan Manuel Debernardi (jmdebernardi{at}ucdavis.edu).