Abstract
BackgroundInflorescences of wheat species, spikes, are characteristically unbranched and bear one sessile spikelet at a spike rachis node. Development of supernumerary spikelets (SSs) at rachis nodes or on the extended rachillas is abnormal. Various wheat morphotypes with altered spike morphology, associated with the development of SSs, present an important genetic resource for studies on genetic regulation of wheat inflorescence development.ResultsHere we characterized diploid and tetraploid wheat lines of various non-standard spike morphotypes, which allowed for identification of a new mutant allele of the WHEAT FRIZZY PANICLE (WFZP) gene that determines spike branching in diploid wheat Ttiticum monococcum L. Moreover, we found that the development of SSs and spike branching in wheat T. durum Desf. was a result of a wfzp-A/TtBH-A1 mutation that originated from spontaneous hybridization with T. turgidum convar. сompositum (L.f.) Filat. Detailed characterization of the false-true ramification phenotype controlled by the recessive sham ramification 2 (shr2) gene in tetraploid wheat T. turgidum L. allowed us to suggest putative functions of the SHR2 gene that may be involved in the regulation of spikelet meristem fate and in specification of floret meristems. The results of a gene interaction test suggested that genes WFZP and SHR2 function independently in different processes during spikelet development, whereas another spike ramification gene(s) interact(s) with SHR2 and share(s) common functions.ConclusionsSS mutants represent an important genetic tool for research on the development of the wheat spikelet and for identification of genes that control meristem activities. Further studies on different non-standard SS morphotypes and wheat lines with altered spike morphology will allow researchers to identify new genes that control meristem identity and determinacy, to elucidate the interaction between the genes, and to understand how these genes, acting in concert, regulate the development of the wheat spike.
Highlights
Inflorescences of wheat species, spikes, are characteristically unbranched and bear one sessile spikelet at a spike rachis node
Standard wheat inflorescence, the spike, consists of sessile spikelets that are directly attached to the spike rachis in the distichous order, one spikelet per a rachis node
The spikelet is a short branch, bearing florets; a spikelet consists of two glumes and 2–5 florets arranged along a spikelet rachilla
Summary
Inflorescences of wheat species, spikes, are characteristically unbranched and bear one sessile spikelet at a spike rachis node. All T. turgidum branching forms have a common spike phenotype: additional spikelets develop on branches and directly at rachis nodes in the lower one-third of the spike; this spike phenotype is often referred to as the turgidum type of branching. In another tetraploid species, T. durum Desf. Coffman [7] has described spontaneous mutants with SSes that have been found in the Mindum durum wheat variety These mutants are characterized by the occurrence of one or two additional sessile spikelets at several rachis nodes in the lower part of the spike; the phenotype is different from the turgidum spike branching. Forms with spike branching and sessile SSes have been found in tetraploid T. dicoccum (Schrank) Schuebl. and occasionally in T. polonicum L. species [6]
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