The role of puroindoline A and B upon grain endosperm texture, end-use quality traits and physicochemical association to starch

by Wanjugi, Humphrey Wainaina.

Endosperm texture in wheat (Triticum aestivum L.) is controlled by the Pina and Pinb genes that together comprise the Hardness (Ha) locus, and is an important criterion affecting end-product quality. The Ha encodes friabilin, a 15 kD protein primarily composed of Puroindoline A (PINA) and Puroindoline B (PINB). Both PINA and PINB interact with starch leading to a soft endosperm, but the physicochemical mechanism controlling endosperm texture is not clearly understood. Here, I isolated the role of PINA and PINB individually and in combination upon grain hardness, milling and bread baking traits. I also determined the effect of overexpressing PINA or PINB on starch bound polar lipids and PIN cellular localization. F3 recombinants homozygous for either the Pina or Pinb null Ha locus with or lacking a transgenically added Pina or Pinb were analyzed for grain hardness, PIN abundance, milling and baking traits, and levels of starch and flour polar lipids. Addition of Pina to the Pinb null Ha locus or Pinb to the Pina null Ha locus resulted in intermediate texture. Genotypes with added Pina to Pina null Ha locus and Pinb to Pinb null Ha locus were soft textured and had low flour yield, ash, small flour particles sizes, and increased PIN and polar lipid levels on starch. PINs localized to the starch granule surface in the presence or absence of the other protein but addition of Pinb to Pina null Ha locus resulted in more PINB associated to starch, increased affinity to bound polar lipids and greater negative effects on baking traits than addition of PINA. Results indicate that overexpression of PINs leads to reduced grain hardness, modified flour milling properties, negatively effects baking traits, and increased starch bound polar lipids. Further, PINA or PINB can act and localize to starch independently of the other protein leading to intermediate texture but soft texture requires both PINA and PINB but, PINB associates more with polar lipids on starch surface and negatively affect baking traits than PINA. My study shows that polar lipids mediate puroindolines association to starch and this mediation can influence endosperm texture, milling, and baking traits. 1