The impact of the SSIIa <i>null</i> mutations on grain traits and composition in durum wheat

Abstract

Starch represents a major nutrient in the human diet providing essentially a source of energy. More recently the modification of its composition has been associated with new functionalities both at the nutritional and technological level. Targeting the major starch biosynthetic enzymes has been shown to be a valuable strategy to manipulate the amylose-amylopectin ratio in reserve starch. In the present work a breeding strategy aiming to produce a set of SSIIa (starch synthases IIa) null durum wheat is described. We have characterized major traits such as seed weight, total starch, amylose, protein and β-glucan content in a set of mutant families derived from the introgression of the SSIIa null trait into Svevo, an elite Italian durum wheat cultivar. A large degree of variability was detected and used to select wheat lines with either improved quality traits or agronomic performances. Semolina of a set of two SSIIa null lines showed new rheological behavior and an increased content of all major dietary fiber components, namely arabinoxylans, β-glucans and resistant starch. Furthermore the investigation of gene expression highlighted important differences in some genes involved in starch and β-glucans biosynthesis.

Novel ssIIa Alleles Produce Specific Seed Amylose Levels in Hexaploid Wheat

“…Yield reductions in ssIIa triple mutant lines are most easily explained by the significant reduction in starch and kernel weight for all mutant haplotypes across both years (Table III). A decrease in kernel weight has been reported in ssIIa null lines in barley, bread, and durum wheat (Morell et al 2003; Clarke et al 2008; Konik‐Rose et al 2007; Hogg et al 2015; Rakszegi et al 2015; Botticella et al 2016). Decreases in kernel weight in the high‐amylose lines are attributable to the decrease in starch content evident in the positive correlation between kernel weight and starch content ( r = 0.70) (Tables III and IV).…”

“…The effect of increased amylose upon wheat kernel hardness is not well described. In durum wheat, which lacks the Ha locus and is the hardest class of wheat, Hogg et al (2015) found a ssIIa null line with increased amylose remained very hard but was significantly softer in kernel texture compared with its wild‐type sister line, whereas Botticella et al (2016) found no correlation between amylose content and grain hardness. In “waxy” durum wheats, which lack amylose owing to wx‐1 null mutations, results are also mixed, with Vignaux et al (2004) finding no relationship between amylose and grain hardness, whereas Grant et al (2004) found the wx‐1 null lines were softer compared with control cv.…”

“…Increases in wheat amylose content have also been achieved by combining natural or induced mutations of starch synthase IIa ( ssIIa ), producing bread and durum wheat with starch amylose content ranging from 35 to 48% (Yamamori et al 2000; Konik‐Rose et al 2007; Lafiandra et al 2010; Shimbata et al 2012; Hogg et al 2013; Rakszegi et al 2015; Botticella et al 2016), and mutant ssIIa lines in barley had amylose between 35 and 70% (Morell et al 2003; Sparla et al 2014). As with the sbeIIa and sbeIIa / b null lines, similar pleiotropic effects are seen in ssIIa null lines with deformed starch granules, reduced starch content and individual kernel weight, reduced flour swelling, and increased grain protein and RS.…”

Milling and baking quality of hexaploid spring wheat starch synthase IIa (ssIIa) mutants with elevated amylose content

“…The increase in sucrose SRCs for ssIIa mutants indicates elevated levels of non‐starch polysaccharides in the flour (Kweon et al, ). The increase in non‐starch polysaccharides can partially be attributed to the increased bran in the flour but elevated levels of other polysaccharides such as fructan, arabinoxylan, and beta‐glucan have been reported in SSIIa nulls in hexaploid wheat, durum wheat, and barley (Clarke et al, , Shimbata et al, , Botticella et al, ; Li et al, ; Botticella et al, ). Lactic acid SRCs showed there was an increase in absorption in ssIIa mutant combinations 1 and 2 compared to controls but similar values between mutant and wild type for combinations 3 and 4, which would indicate the functionality of gluten in ssIIa mutants and wild types, are comparable when analyzed independently (Kweon et al, ).…”

“…Similar results have been observed in durum wheat ( Triticum turgidum sp . durum ) (Botticella et al, ; Hogg et al, ; Hogg, Martin, Manthey, & Giroux, ) and barley ( Hordeum vulgare ) (Morell et al, , Clarke et al, , Regina et al, , Sparla et al, ).…”