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Spike density and processing quality are important traits in modern wheat production and are controlled by multiple gene loci. The associated genes have been intensively studied and new discoveries have been constantly reported during the past few decades. However, no gene playing a significant role in the development of these two traits has been identified. In the current study, a common wheat mutant with extremely compact spikes and good processing quality was isolated and characterized. A new allele (Qc1) of the Q gene (an important domestication gene) responsible for the mutant phenotype was cloned, and the molecular mechanism for the mutant phenotype was studied. Results revealed that Qc1 originated from a point mutation that interferes with the miRNA172-directed cleavage of Q transcripts, leading to its overexpression. It also reduces the longitudinal cell size of rachises, resulting in an increased spike density. Furthermore, Qc1 increases the number of vascular bundles, which suggests a higher efficiency in the transportation of assimilates in the spikes of the mutant than that of wild type. This accounts for the improved processing quality. The effects of Qc1 on spike density and wheat processing quality were confirmed by analyzing nine common wheat mutants possessing four different Qc alleles. These results deepen our understanding of the key roles of Q gene, and provide new insights for the potential application of Qc alleles in wheat quality breeding.

Little is known about the relationship between compact spike loci in hexaploid wheat species. We studied two new compact spike mutants of common wheat Triticum aestivum L. (2 n = 6 x = 42, genome formula BBAADD). The new compact spike genes, C of MCK 739 and Cp of near-isogenic line Mironovskaya 808 ( Vrn1), were mapped using aneuploid stocks and microsatellite markers. The C and Cp loci were distally linked with the microsatellite marker Xbarc319 in the F populations of MCK 739 × 'Novosibirskaya 67' and Cp-Mironovskaya 808 ( Vrn1) × 'Saratovskaya 29'. It was evident that the loci affecting compact spikes in T. aestivum mutants were located on chromosome 5AL distal from Q locus. These loci also affected to semi-dwarfism. We named this locus Cp1 ( C ompact p lant 1) for all accessions. Cp1 was allelic to C gene located on the chromosome 5AL of tetraploid wheat [ Triticum durum Desf. (2 n = 4 x = 28, genome formula BBAA)]. These dominant genes on chromosome 5AL will be utilized as new gene resources of compact spike morphology in hexaploid wheat. Relationship between loci Q and Cp1 was also discussed. [ABSTRACT FROM AUTHOR]

Two mutants for sphaerococcoid seed (MA 16219) and compact spike (MA 17648) were isolated from M3 progeny of durum wheat cultivar, Altaiskaya Niva, mutagenized with chemical mutagens. The chromosomal locations of the genes involved were determined by the use of a complete set of D-genome disomic substitutions in durum cultivar, Langdon. The gene for sphaerococcoid grain, s 16219 , was allelic to S2, located in the centromeric region of chromosome 3B in hexaploid wheat. The gene for compact spike, C 17648 , was located on chromosome 5AL distal to the Q locus. Using microsatellite markers, C 17648 and awn inhibitor B1 were located in the F2 of LD222 × MA17648. The gene order was Xbarc319— C 17648 — Xgwm179— Xgwm126—Xgwm291— B1. [ABSTRACT FROM AUTHOR]

Spike density and processing quality are important traits in modern wheat production and are controlled by multiple gene loci. The associated genes have been intensively studied and new discoveries have been constantly reported during the past few decades. However, no gene playing a significant role in the development of these two traits has been identified. In the current study, a common wheat mutant with extremely compact spikes and good processing quality was isolated and characterized. A new allele ( Q c1 ) of the Q gene (an important domestication gene) responsible for the mutant phenotype was cloned, and the molecular mechanism for the mutant phenotype was studied. Results revealed that Q c1 originated from a point mutation that interferes with the miRNA172-directed cleavage of Q transcripts, leading to its overexpression. It also reduces the longitudinal cell size of rachises, resulting in an increased spike density. Furthermore, Q c1 increases the number of vascular bundles, which suggests a higher efficiency in the transportation of assimilates in the spikes of the mutant than that of wild type. This accounts for the improved processing quality. The effects of Q c1 on spike density and wheat processing quality were confirmed by analyzing nine common wheat mutants possessing four different Q c alleles. These results deepen our understanding of the key roles of Q gene, and provide new insights for the potential application of Q c alleles in wheat quality breeding., (Copyright © 2018 Xu et al.)