Co-suppression of synthesis of major α-kafirin sub-class together with γ-kafirin-1 and γ-kafirin-2 required for substantially improved protein digestibility in transgenic sorghum

Abstract

The combined suppression of only two genes, γ kafirin-1 (25 kDa) and γ-kafirin-2 (50 kDa), significantly increases sorghum kafirin in vitro digestibility. Co-suppression of a third gene, α-kafirin A1 (25 kDa), in addition to the two genes increases the digestibility further. The high-digestibility trait has previously only been obtained either through the co-suppression of six kafirin genes (α-A1, 25 kDa; α-B1, 19 kDa; α-B2, 22 kDa; γ-kaf1, 27 kDa; γ-kaf 2, 50 kDa; and δ-kaf 2, 18 kDa) or through random chemical-induced mutations (for example, the high protein digestibility mutant). We present further evidence that suppressing just three of these genes alters kafirin protein cross-linking and protein body microstructure to an irregularly invaginated phenotype. The irregular invaginations are consistent with high pepsin enzyme accessibility and hence high digestibility. The approach we adopted towards increasing sorghum protein digestibility appears to be an effective tool in improving the status of sorghum as a principal supplier of energy and protein in poor communities residing in marginal agro-ecological zones of Africa.

Functionality of the storage proteins in gluten-free cereals and pseudocereals in dough systems

“…However, their actual dough properties and leavened bread-making quality were not investigated. Kumar et al (2012), in general agreement with the findings of Da Silva et al (2011a) and Grootboom et al (2014), showed that γ-kafirin suppression alone did not alone alter protein body structure, but attributed this to the silencing of a predicted 29 kDa α-kafirin sub-class (presumably a cysteine-poor protein). With the aim of improving the roti (flatbread) making quality of sorghum, gene cassettes containing a wheat HMW-GS gene driven by the γ-kafirin promoter have been constructed (Mishra et al, 2008).…”

“…Da Silva et al (2011a) and Grootboom et al (2014) showed that co-suppression of the synthesis of α-, γ-, β-and δ-kafirins modified the structure of the protein bodies so that they had invaginations like those of the high protein digestibility mutant (Oria et al, 2000) and that they were less densely packed in the endosperm. These changes resulted in the endosperm structure becoming floury.…”

A Comparative Study of Selected Physical and Biochemical Traits of Wild-Type and Transgenic Sorghum to Reveal Differences Relevant to Grain Quality

“…Previous analyses found complete suppression of the targeted kafirin proteins and a significant improvement (of up to 37%) in the in vitro protein digestibility of the transgenic grains (Grootboom et al, 2014). The transgenic lines represent the fifth generation of self-crossing progenies from T 0 sorghum transformants, which were originally produced using particle bombardment as described in Grootboom et al (2014).…”

“…Previous analyses found complete suppression of the targeted kafirin proteins and a significant improvement (of up to 37%) in the in vitro protein digestibility of the transgenic grains (Grootboom et al, 2014). The transgenic lines represent the fifth generation of self-crossing progenies from T 0 sorghum transformants, which were originally produced using particle bombardment as described in Grootboom et al (2014). Plants from each independent transgenic line (hereafter referred to as 42-1 and 42-2) and the parental control cultivar P898012 (hereafter referred to as WT), were grown in pots in a containment glasshouse located at the Centre for Scientific and Industrial Research (CSIR) Biosciences Division (Pretoria, South Africa).…”

“…Grootboom et al (2014), used RNA interference (RNAi) technology to suppress the expression of select kafirin subclasses, which resulted in transgenic sorghum grain with improved protein digestibility levels of up to 53%. Although, this approach has been recognized as an effective strategy for increasing the protein digestibility (and hence the nutritional value) of sorghum grain, these “improved” transgenic lines have not yet been commercialized or cultivated.…”