Genetic analysis of grain protein content and deviation in wheat

Grain protein content (GPC) is generally inversely correlated with grain yield (GY) but some genotypes consistently have higher grain protein contents than predicted by simple regression analysis: this is called grain protein deviation (GPD). GPD reflects greater nitrogen use efficiency and is an important target for breeders to develop more sustainable types of wheat. Here, we investigate the genetic architecture of GPC, GY, thousand grain weight (TGW) and GPD using a population of 104 doubled haploid lines derived from a cross between two cultivars with positive (Hereward) and negative (Malacca) GPD and grown in replicated randomised field trials over three years. A total of 9 QTL were detected for all traits, five for GPC, two for GPD and one each for GY and TGW. All of the increasing alleles for GPC and GPD and for the single QTL for TGW were contributed by Hereward while Malacca contributed the single increasing allele for GY. The two QTLs for GPD located on chromosomes 3A and 5B explained 23.3% and 16.6% of the variance in the sample sets, respectively. Three QTL for GPC (on chromosomes 3A, 3B, 5B) each explained more than 14% of the variance, with those on chromosomes 3A and 5B having similar locations to the GPC QTLs on the same chromosomes. A survey of the gene content between the markers bordering the confidence intervals for the two GPD QTLs on chromosomes 3A and 5B identified 136 and 704 protein coding genes, respectively, including possible candidate genes

TEOSINTE BRANCHED1 regulates height and stem internode length in bread wheat

Regulation of plant height and stem elongation has contributed significantly to improvement of cereal productivity by reducing lodging and improving distribution of assimilates to the inflorescence and grain. In wheat, genetic control of height has been largely contributed by the Reduced height-1 alleles that confer gibberellin insensitivity; the beneficial effects of these alleles are associated with less favourable effects involving seedling emergence, grain quality, and inflorescence architecture that have driven new research investigating genetic variation of stem growth. Here, we show that TEOSINTE BRANCHED1 (TB1) regulates height of wheat, with TB1 being expressed at low levels in nodes of the main culm prior to elongation, and increased dosage of TB1 restricting elongation of stem internodes. The effect of TB1 on stem growth is not accompanied by poor seedling emergence, as transgenic lines with increased activity of TB1 form longer coleoptiles than null transgenic controls. Analysis of height in a multiparent mapping population also showed that allelic variation for TB1 on the B genome influences height, with plants containing the variant TB-B1b allele being taller than those with the wild-type TB-B1a allele. Our results show that TB1 restricts height and stem elongation in wheat, suggesting that variant alleles that alter the expression or function of TB1 could be used as a new source of genetic diversity for optimizing architecture of wheat in breeding programmes