Recent advances in the study of prolamin storage protein organization and function

Abstract

Prolamin storage proteins are the main repository for nitrogen in the endosperm of cereal seeds. These stable proteins accumulate at massive levels due to the high level expression from extensively duplicated genes in endoreduplicated cells. Such abundant accumulation is achieved through efficient packaging in endoplasmic reticulum localized protein bodies in a process that is not completely understood. Prolamins are also a key determinant of hard kernel texture in the mature seed; an essential characteristic of cereal grains like maize. However, deficiencies of key essential amino acids in prolamins result in relatively poor grain protein quality. The inverse relationship between prolamin accumulation and protein quality has fueled an interest in understanding the role of prolamins and other proteins in endosperm maturation. This article reviews recent technological advances that have enabled dissection of overlapping and non-redundant roles of prolamins, particularly the maize zeins. This has come through molecular characterization of mutants first identified many decades ago, selective down-regulation of specific zein genes or entire zein gene families, and most recently through combining deletion mutagenesis with current methods in genome and transcriptome profiling. Works aimed at understanding prolamin deposition and function as well as creating novel variants with improved nutritional and digestibility characteristics, are reported.

Glutelin is partially degraded in globulin-less mutants of rice (Oryza sativaL.)

“…In this study, however, globulin-less mutation was unique to induce partial degradation of glutelin rather than compensation. Although compositional change of protein bodies induced by RNAi was demonstrated to result in irregular structure of PB in maize (Holding, 2014), wheat (Gil-Humanes et al, 2011), and rice (Kawakatsu et al, 2010;Nagamine et al, 2011), partial degradation has not ever been reported. Considering our results together with the fact that globulin accumulates on the surface of PB-II (Krishnan et al, 1992;Kumamaru et al, 2010) and its absence results in structurally deformed PB-II (Ashida et al, 2011), globulin protects glutelins from proteinase digestion and thereby facilitates stable glutelin accumulation.…”

Quality protein maize (QPM): Genetic basis and breeding perspective

“…It seems that developing maize seeds possess compensatory mechanisms that sense protein content when zein synthesis is interrupted, leading to translation of other mRNAs instead of zein mRNAs. Combining deletion mutagenesis with current methods in genome and transcriptome profiling can make it possible to reveal alteration in amino acid composition (Holding 2014). RNA interference based down regulation of 22kD RNAi lines is reported to cause opaque phenotype more profoundly as compared to 19kD component.…”

Size-controlled fabrication of zein nano/microparticles by modified anti-solvent precipitation with/without sodium caseinate

“…Zein is primarily present as protein bodies in endosperm cells and can be extracted and separated with various technologies. 6,7 According to solubility and sequence similarity, zein can be further divided into α-, β-, γ-, and δ-zeins. Among these, α-zein accounts for the largest fraction (approximately 80%) of the total zein mass.…”