ABSTRACT''Soft'' and ''hard'' are the two main market classes of wheat (Triticum aestivum L.) and are distinguished by expression of the Hardness gene. Friabilin, a marker protein for grain softness (Ha), consists of two proteins, puroindoline a and b (pinA and pinB, respectively). We previously demonstrated that a glycine to serine mutation in pinB is linked inseparably to grain hardness. Here, we report that the pinB serine mutation is present in 9 of 13 additional randomly selected hard wheats and in none of 10 soft wheats. The four exceptional hard wheats not containing the serine mutation in pinB express no pinA, the remaining component of the marker protein friabilin. The absence of pinA protein was linked inseparably to grain hardness among 44 near-isogenic lines created between the soft variety Heron and the hard variety Falcon. Both pinA and pinB apparently are required for the expression of grain softness. The absence of pinA protein and transcript and a glycine-to-serine mutation in pinB are two highly conserved mutations associated with grain hardness, and these friabilin genes are the suggested tightly linked components of the Hardness gene. A previously described grain hardness related gene termed ''GSP-1'' (grain softness protein) is not controlled by chromosome 5D and is apparently not involved in grain hardness. The association of grain hardness with mutations in both pinA or pinB indicates that these two proteins alone may function together to effect grain softness. Elucidation of the molecular basis for grain hardness opens the way to understanding and eventually manipulating this wheat endosperm property.

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Kernel morphology and texture influence the value of wheat (Triticum aestivum L.). The objectives of this study were to determine associations between kernel traits and molecular markers and to identify quantitative trait loci (QTLs) affecting kernel traits in a soft × hard white wheat cross. Seventy eight F~-derived recombinant inbred lines (RILs) from cross be tween the so ft wh ite wh eat NY 6432-18 (NY18) and the hard white wheat 'Clark's Cream' (CC) were developed by single seed descent. Kernel texture was measured by near infrared reflectance (NIR) on RIL grain samples from six environments. Digital image analysis (DIA) was used to measure kernel length, width, area, perimeter on grain samples from four environments. Test weight and thousand kernel weight (TKW) were also determined. Shape factor and density factor were calculated. The map for this population consisted of 313 molecular markers in 47 linkage groups located on all wheat homoeologous chromosome groups. Linkage groups that mapped to wheat homoeologous group 2 chromosomes were highly skewed towards NY18 alleles. Genotype effects and genotype × environment interactions were highly significant for most traits. QTLs for kernel width and kernel length also influenced kernel area and TKW, but did not influence each other. The pinB marker at the puroindoline B locus on chromosome 5DS explained over 60% of the phenotypic variation for kernel texture. QTLs for kernel traits were located on chromosomes IA, 2B, 2D, 3B, 7A, and 7B. Tm HE ECONOMIC VALUE of the U.S. wheat crop is deterined by class, which depends in part on kernel morphology and texture, and by test weight. Inspectors for the U.S. Grain Inspection, Packers and Stockyards Administration use color, shape, and length of the kernel and shape of the germ, crease, and brush to determine wheat grain classes (GIPSA, 1997). In general, hard wheat kernels are long, narrow, and translucent while soft kernels are short, rounded, and chalky in appearance. Hybridization between classes reduces the correlation between kernel morphology and wheat class and reduces the accuracy of the current classification

Yield in cereals is a function of seed number and weight; both parameters are largely controlled by seed sink strength. The allosteric enzyme ADP-glucose pyrophosphorylase (AGP) plays a key role in regulating starch biosynthesis in cereal seeds and is likely the most important determinant of seed sink strength. Plant AGPs are heterotetrameric, consisting of two large and two small subunits. We transformed wheat (Triticum aestivum L.) with a modified form of the maize (Zea mays L.) Shrunken2 gene (Sh2r6hs), which encodes an altered AGP large subunit. The altered large subunit gives rise to a maize AGP heterotetramer with decreased sensitivity to its negative allosteric effector, orthophosphate, and more stable interactions between large and small subunits. The Sh2r6hs transgene was still functional after five generations in wheat. Developing seeds from Sh2r6hs transgenic wheat exhibited increased AGP activity in the presence of a range of orthophosphate concentrations in vitro. Transgenic Sh2r6hs wheat lines produced on average 38% more seed weight per plant. Total plant biomass was increased by 31% in Sh2r6hs plants. Results indicate increased availability and utilization of resources in response to enhanced seed sink strength, increasing seed yield, and total plant biomass. W heat (Triticum aestivum L.) is one of the world's most important crop plants. An estimated 610 million metric tons of wheat seed were harvested worldwide in the 1997͞98 growing season (1). Wheat seed yield is determined by seed number and weight. Starch is the major component of wheat yield, comprising 70% of wheat seed dry weight. ADP-glucose pyrophosphorylase (AGP; EC 2.7.7.27), an allosterically regulated heterotetramer consisting of two large and two small subunits, catalyzes the rate-limiting reaction in starch biosynthesis in plants (reviewed in refs. 2 and 3). AGP uses the substrates glucose 1-phosphate and ATP to produce ADPglucose and pyrophosphate (4). ADP-glucose is then used as the glucose donor for starch synthases. The positive allosteric effector of AGP is 3-phosphoglycerate, whereas the negative allosteric effector is orthophosphate (Pi) (2, 3). Maize endosperm AGP (5) large subunits are encoded by Shrunken2 (Sh2) (6), whereas small subunits are encoded by Brittle2 (Bt2) (7).Inhibition of AGP activity by Pi appears to limit starch biosynthesis and yield in crop plants. Evidence for this has come from studies of a modified AGP large subunit in maize (8) and from use of an altered bacterial AGP in potato (9). In both cases, AGP modification caused reduced sensitivity to Pi inhibition, resulting in enhanced yield, manifested as increased seed weight in maize (8) and increased starch content in potato (9). Instability of AGP may be an additional limitation on cereal yield. AGP is perhaps the most heat-labile starch biosynthetic enzyme in maize (10-12). A single amino acid substitution in the maize large subunit that conditions more stable large subunit-small subunit interactions (13) may lead to enhanced AGP activity and increa...