Wheat ms5 male-sterility is induced by recessive homoeologous A and D genome non-specific lipid transfer proteins.

Nuclear male-sterile mutants with non-conditional, recessive and strictly monogenic inheritance are useful for both hybrid and conventional breeding systems, and have long been a research focus for many crops. In allohexaploid wheat, however, genic redundancy results in rarity of such mutants, with the ethyl methanesulfonate-induced mutant ms5 among the few reported to date. Here, we identify TaMs5 as a glycosylphosphatidylinositol-anchored lipid transfer protein required for normal pollen exine development, and by transgenic complementation demonstrate that TaMs5-A restores fertility to ms5. We show ms5 locates to a centromere-proximal interval and has a sterility inheritance pattern modulated by TaMs5-D but not TaMs5-B. We describe two allelic forms of TaMs5-D, one of which is non-functional and confers mono-factorial inheritance of sterility. The second form is functional but shows incomplete dominance. Consistent with reduced functionality, transcript abundance in developing anthers was found to be lower for TaMs5-D than TaMs5-A. At the 3B homoeolocus, we found only non-functional alleles among 178 diverse hexaploid and tetraploid wheats that include landraces and Triticum dicoccoides. Apparent ubiquity of non-functional TaMs5-B alleles suggests loss-of-function arose early in wheat evolution and, therefore, at most knockout of two homoeoloci is required for sterility. This work provides genetic information, resources and tools required for successful implementation of ms5 sterility in breeding systems for bread and durum wheats.

Effects of Rht-B1 and Ppd-D1 loci on pollinator traits in wheat.

KEY MESSAGE: Elite wheat pollinators are critical for successful hybrid breeding. We identified Rht-B1 and Ppd-D1 loci affecting multiple pollinator traits and therefore represent major targets for improving hybrid seed production. Hybrid breeding has a great potential to significantly boost wheat yields. Ideal male pollinators would be taller in stature, contain many spikelets well-spaced along the spike and exhibit high extrusion of large anthers. Most importantly, flowering time would match with that of the female parent. Available genetic resources for developing an elite wheat pollinator are limited, and the genetic basis for many of these traits is largely unknown. Here, we report on the genetic analysis of pollinator traits using biparental mapping populations. We identified two anther extrusion QTLs of medium effect, one on chromosome 1BL and the other on 4BS coinciding with the semi-dwarfing Rht-B1 locus. The effect of Rht-B1 alleles on anther extrusion is genotype dependent, while tall plant Rht-B1a allele is consistently associated with large anthers. Multiple QTLs were identified at the Ppd-D1 locus for anther length, spikelet number and spike length, with the photoperiod-sensitive Ppd-D1b allele associated with favourable pollinator traits in the populations studied. We also demonstrated that homeoloci, Rht-D1 and Ppd-B1, influence anther length among other traits. These results suggest that combinations of Rht-B1 and Ppd-D1 alleles control multiple pollinator traits and should be major targets of hybrid wheat breeding programs.

Wheat TaMs1 is a glycosylphosphatidylinositol-anchored lipid transfer protein necessary for pollen development.

BACKGROUND: In flowering plants, lipid biosynthesis and transport within anthers is essential for male reproductive success. TaMs1, a dominant wheat fertility gene located on chromosome 4BS, has been previously fine mapped and identified to encode a glycosylphosphatidylinositol (GPI)-anchored non-specific lipid transfer protein (nsLTP). Although this gene is critical for pollen exine development, details of its function remains poorly understood. RESULTS: In this study, we report that TaMs1 is only expressed from the B sub-genome, with highest transcript abundance detected in anthers containing microspores undergoing pre-meiosis through to meiosis. ß-glucuronidase transcriptional fusions further revealed that TaMs1 is expressed throughout all anther cell-types. TaMs1 was identified to be expressed at an earlier stage of anther development relative to genes reported to be necessary for sporopollenin precursor biosynthesis. In anthers missing a functional TaMs1 (ms1c deletion mutant), these same genes were not observed to be mis-regulated, indicating an independent function for TaMs1 in pollen development. Exogenous hormone treatments on GUS reporter lines suggest that TaMs1 expression is increased by both indole-3-acetic acid (IAA) and abscisic acid (ABA). Translational fusion constructs showed that TaMs1 is targeted to the plasma membrane. CONCLUSIONS: In summary, TaMs1 is a wheat fertility gene, expressed early in anther development and encodes a GPI-LTP targeted to the plasma membrane. The work presented provides a new insight into the process of wheat pollen development.

Unfertilized ovary pushes wheat flower open for cross-pollination.

Bread wheat is strongly autogamous; however, an opportunity for outcrossing occurs when self-pollination fails and florets open. The first phase of floret opening at anthesis is short and induced by lodicule turgidity. Some wheat florets re-open post-anthesis for several days, known as the 'second opening', for which the underlying mechanisms are largely unknown. We performed detailed physiological, anatomical, and histological investigations to understand the biological basis of the flower opening process. Wheat florets were observed open when the ovary was unfertilized. Unfertilized ovaries significantly increased in radial size post-anthesis, pushing the lemma and palea apart to open the florets. The absence of fertile pollen was not directly linked to this, but anther filament elongation coincided with initiation of ovary swelling. The pericarp of unfertilized ovaries did not undergo degeneration as normally seen in developing grains, instead pericarp cells remained intact and enlarged, leading to increased ovary radial size. This is a novel role for the ovary pericarp in wheat flower opening, and the knowledge is useful for facilitating cross-pollination in hybrid breeding. Ovary swelling may represent a survival mechanism in autogamous cereals such as wheat and barley, ensuring seed set in the absence of self-fertilization and increasing genetic diversity through cross-pollination.

Expression of flavonoid 6-hydroxylase candidate genes in normal and mutant soybean genotypes for glycitein content.

Soybean seeds accumulate large amounts of isoflavones (genistein, daidzein and glycitein), secondary metabolites known for their phytoestrogenic activities. Isoflavone composition depends on the seed part and glycitein is almost found exclusively in hypocotyls. Moreover, two major phenotypes are encountered in soybean cultivars, with either low (35 %) or high (55 %) levels of glycitein in their hypocotyls. This trait was under a quasi-mendelian heredity, implicating at most one or two genes. A CYP71D9 cDNA displaying a flavonoid 6-hydroxylase (F6H) activity had previously been isolated from elicitor-induced soybean (Glycine max L.) cells. This enzyme allows the synthesis of the glycitein flavanone intermediate (6,7,4'- trihydroxyflavanone) by catalyzing the A-ring hydroxylation of liquiritigenin. In this study, the CYP71D9 gene (F6H1) and two other candidates (F6H2 and F6H3) were studied using contrasted soybean cultivars for glycitein content (0, 35, 55 and 80 %). Their expression was observed in chitosan elicited leaves. They encode P450 proteins of 496, 469 and 481 amino acids respectively and were expressed in leaves with or without elicitation. The expression patterns of these three genes were performed in cotyledons and hypocotyls at different developmental stages. F6H1 and F6H2 were not expressed in the developing seed. F6H3 was only expressed in hypocotyls. Its expression levels did not correlate with hypocotyls glycitein content, but it was not expressed in the null mutant for glycitein. Thus, this F6H3 gene is a good potential candidate for glycitein biosynthesis in soybean seed.

Molecular identification of the wheat male fertility gene Ms1 and its prospects for hybrid breeding.

The current rate of yield gain in crops is insufficient to meet the predicted demands. Capturing the yield boost from heterosis is one of the few technologies that offers rapid gain. Hybrids are widely used for cereals, maize and rice, but it has been a challenge to develop a viable hybrid system for bread wheat due to the wheat genome complexity, which is both large and hexaploid. Wheat is our most widely grown crop providing 20% of the calories for humans. Here, we describe the identification of Ms1, a gene proposed for use in large-scale, low-cost production of male-sterile (ms) female lines necessary for hybrid wheat seed production. We show that Ms1 completely restores fertility to ms1d, and encodes a glycosylphosphatidylinositol-anchored lipid transfer protein, necessary for pollen exine development. This represents a key step towards developing a robust hybridization platform in wheat.Heterosis can rapidly boost yield in crop species but development of hybrid-breeding systems for bread wheat remains a challenge. Here, Tucker et al. describe the molecular identification of the wheat Ms1 gene and discuss its potential for large-scale hybrid seed production in wheat.