MORE SPIKELETS1 Is Required for Spikelet Fate in the Inflorescence of Brachypodium

• Published in: Plant physiology (Bethesda) Vol. 161; no. 3; pp. 1291 - 1302
• Main Authors: Derbyshire, Paul, Byrne, Mary E.
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.03.2013
• Subjects: Amino Acid Sequence; Barley; Base Sequence; Biological and medical sciences; Brachypodium - growth & development; Brachypodium - ultrastructure; Chromosomes, Plant - metabolism; Corn; Developmental biology; Florets; Fundamental and applied biological sciences. Psychology; Gene Rearrangement - genetics; Genes; GENES, DEVELOPMENT, AND EVOLUTION; Genes, Plant - genetics; Inflorescence - growth & development; Inflorescence - ultrastructure; Inflorescences; Meristems; Molecular Sequence Data; Mutagenesis - genetics; Mutation - genetics; Plant physiology and development; Plant Proteins - chemistry; Plant Proteins - genetics; Plant Proteins - metabolism; Plants; Reproduction; Rice; Spikelets; Transcription Factors - metabolism; Monocotyledones; Spikelets; Plant physiology; Gramineae; Inflorescence; Angiospermae; Spermatophyta
• DOI: 10.1104/pp.112.212340
• ISSN: 0032-0889; 1532-2548

Grasses produce florets on a structure called a spikelet, and variation in the number and arrangement of both branches and spikelets contributes to the great diversity of grass inflorescence architecture. In Brachypodium (Brachypodium distachyori), the inflorescence is an unbranched spike with a terminal spikelet and a limited number of lateral spikelets. Spikelets are indeterminate and give rise to a variable number of florets. Here, we provide a detailed description of the stages of inflorescence development in Brachypodium. To gain insight into the genetic regulation of Brachypodium inflorescence development, we generated fast neutron mutant populations and screened for phenotypic mutants. Among the mutants identified, the more spikelets1 (mos1) mutant had an increased number of axillary meristems produced from inflorescence meristem compared with the wild type. These axillary meristems developed as branches with production of higher order spikelets. Using a candidate gene approach, mos1 was found to have a genomic rearrangement disrupting the expression of an ethylene response factor class of APETALA2 transcription factor related to the spikelet meristem identity genes branched silklessl (bdl) in maize (Zea mays) and FRIZZY PANICLE (FZP) in rice (Oryza sativa). We propose MOS1 likely corresponds to the Brachypodium bd1 and FZP ortholog and that the function of this gene in determining spikelet meristem fate is conserved with distantly related grass species. However, MOS1 also appears to be involved in the timing of initiation of the terminal spikelet. As such, MOS1 may regulate the transition to terminal spikelet development in other closely related and agriculturally important species, particularly wheat (Triticum aestivum).