The wheat Phs-A1 pre-harvest sprouting resistance locus delays the rate of seed dormancy loss and maps 0.3 cM distal to the PM19 genes in UK germplasm.

The precocious germination of cereal grains before harvest, also known as pre-harvest sprouting, is an important source of yield and quality loss in cereal production. Pre-harvest sprouting is a complex grain defect and is becoming an increasing challenge due to changing climate patterns. Resistance to sprouting is multi-genic, although a significant proportion of the sprouting variation in modern wheat cultivars is controlled by a few major quantitative trait loci, including Phs-A1 in chromosome arm 4AL. Despite its importance, little is known about the physiological basis and the gene(s) underlying this important locus. In this study, we characterized Phs-A1 and show that it confers resistance to sprouting damage by affecting the rate of dormancy loss during dry seed after-ripening. We show Phs-A1 to be effective even when seeds develop at low temperature (13 °C). Comparative analysis of syntenic Phs-A1 intervals in wheat and Brachypodium uncovered ten orthologous genes, including the Plasma Membrane 19 genes (PM19-A1 and PM19-A2) previously proposed as the main candidates for this locus. However, high-resolution fine-mapping in two bi-parental UK mapping populations delimited Phs-A1 to an interval 0.3 cM distal to the PM19 genes. This study suggests the possibility that more than one causal gene underlies this major pre-harvest sprouting locus. The information and resources reported in this study will help test this hypothesis across a wider set of germplasm and will be of importance for breeding more sprouting resilient wheat varieties.

Genetic control of storage oil synthesis in seeds of Arabidopsis.

Quantitative trait loci (QTL) that control seed oil content and fatty acid composition were studied using a recombinant inbred population derived from a cross between the Arabidopsis ecotypes Landsberg erecta and Cape Verdi Islands. Multiple QTL model mapping identified two major and two minor QTL that account for 43% of the variation in oil content in the population. The most significant QTL is at the bottom of chromosome 2 and accounts for 17% of the genetic variation. Two other significant QTL, located on the upper and lower arms of chromosome 1, account for a further 19% of the genetic variation. A QTL near to the top of chomosome 3 is epistatic to that on the upper arm of chromosome 1. There are strong QTL for linoleic (18:2) and linolenic (18:3) acids contents that colocate with the FAD3 locus, another for oleic acid (18:1) that colocates with FAD2 and other less significant QTL for palmitic (16:0), stearic (18:0), and eicosaenoic (20:1) acids. The presence of the QTL for seed oil content on chromosome 2 was confirmed by the generation of lines that contain a 22-cM region of Landsberg erecta DNA at the bottom of chromosome 2 in a background containing Cape Verdi Islands in other regions of the genome that had been shown to influence oil content in the QTL analysis.

Transcripts of Vp-1 homeologues are misspliced in modern wheat and ancestral species.

The maize (Zea mays) Viviparous 1 (Vp1) transcription factor has been shown previously to be a major regulator of seed development, simultaneously activating embryo maturation and repressing germination. Hexaploid bread wheat (Triticum aestivum) caryopses are characterized by relatively weak embryo dormancy and are susceptible to preharvest sprouting (PHS), a phenomenon that is phenotypically similar to the maize vp1 mutation. Analysis of Vp-1 transcript structure in wheat embryos during grain development showed that each homeologue produces cytoplasmic mRNAs of different sizes. The majority of transcripts are spliced incorrectly, contain insertions of intron sequences or deletions of coding region, and do not have the capacity to encode full-length proteins. Several VP-1-related lower molecular weight protein species were present in wheat embryo nuclei. Embryos of a closely related tetraploid species (Triticum turgidum) and ancestral diploids also contained misspliced Vp-1 transcripts that were structurally similar or identical to those found in modern hexaploid wheat, which suggests that compromised structure and expression of Vp-1 transcripts in modern wheat are inherited from ancestral species. Developing embryos from transgenic wheat grains expressing the Avena fatua Vp1 gene showed enhanced responsiveness to applied abscisic acid compared with the control. In addition, ripening ears of transgenic plants were less susceptible to PHS. Our results suggest that missplicing of wheat Vp-1 genes contributes to susceptibility to PHS in modern hexaploid wheat varieties and identifies a possible route to increase resistance to this environmentally triggered disorder.