No abstract

For personal use only.

No abstract

The sequence of the puroindoline-b gene from 15 Australian wheat cultivars was determined. Sequence variation was observed in the WPTKWWKGGCE motif of the deduced puroindoline-b protein sequence. Previously, it has been suggested that this sequence is crucial in determining grain hardness. In this study, no correlation was found between the variation in this sequence and the hardness or softness of the cultivar. The amounts of puroindo-line- a and puroindoline-b protein in a selection of hard and soft Australian wheat cultivars were also determined using ELISA techniques. Both soft and hard cultivars had variable amounts of puroindoline-a and puroindoline-b. In particular, it is notable that the hard cultivars Cook and Diaz contained high amounts of puroindoline-a and puroin-doline- b and also contained the puroindoline-b sequence previously reported to be associated with grain softness. These results suggest that if the puroindoline proteins are involved in determining grain softness or hardness they do so as part of a multi-component mechanism.

Genes for puroindoline-a (Pin-a), puroindoline-b (Pin-b) and grain-softness proteins (GSP) have been shown to be linked to the dominant Ha locus responsible for the soft texture of the grain. Though linkage has been demonstrated of the puroindoline genes to the Ha locus, there is no clear evidence that puroindoline content is the product of the gene Ha. A segregating population of 115 recombinant inbred lines (RILs) originating from a cross between the hexaploid Synthetic wheat ( Triticum durum x Aegilops tauschii, W 7984) and the cultivar 'Opata' (M 85) was studied in two different experimental years to detect Quantitative Trait Loci (QTLs) for three traits: grain hardness (Hard), puroindoline-a (Pin-a) and puroindoline-b (Pin-b) contents. The detection of QTLs was performed using marker linear regression. Negative correlation coefficients (-0.86 and -0.80) were identified between grain hardness and puroindoline content (a and b, respectively) on data obtained in 1996. Results obtained in 1999 confirmed the negative correlation between Hard and Pin-a (-0.73); however a positive correlation coefficient was found with Pin-b content (0.41). Total phenotypic variation explained by each QTL was calculated (R2). For each of the Hard, Pin-a and Pin-b traits one major QTL was detected on the short arm of chromosome 5D, located close to the mta9 allele (puroindoline-a). For the first year (1996) the QTL in this region explained around 63% of the phenotypic variability in grain hardness, 77% in Pin-a and 45% in Pin-b contents. These values were confirmed in trials carried out in 1999 with a R2 value of 0.71, 0.72 and 0.25 for Hard, Pin-a and Pin-b, respectively. In 1996 and 1999 a second major QTL was detected for grain hardness on the long arm of the same chromosome. Present results indicate that it cannot be definitely concluded that puroindoline content represents a linear explanation for variations in grain hardness.