The dynamics of protein body formation in developing wheat grain

Katie L Moore,Peter R Shewry,Paola Tosi,Malcolm J Hawkesford,Chris R.M Grovenor,Richard Palmer

doi:10.1111/pbi.12549

Abstract

SummaryWheat is a major source of protein in the diets of humans and livestock but we know little about the mechanisms that determine the patterns of protein synthesis in the developing endosperm. We have used a combination of enrichment with 15N glutamine and NanoSIMS imaging to establish that the substrate required for protein synthesis is transported radially from its point of entrance in the endosperm cavity across the starchy endosperm tissues, before becoming concentrated in the cells immediately below the aleurone layer. This transport occurs continuously during grain development but may be slower in the later stages. Although older starchy endosperm cells tend to contain larger protein deposits formed by the fusion of small protein bodies, small highly enriched protein bodies may also be present in the same cells. This shows a continuous process of protein body initiation, in both older and younger starchy endosperm cells and in all regions of the tissue. Immunolabeling with specific antibodies shows that the patterns of enrichment are not related to the contents of gluten proteins in the protein bodies. In addition to providing new information on the dynamics of protein deposition, the study demonstrates the wider utility of NanoSIMS and isotope labelling for studying complex developmental processes in plant tissues.

Highlights

Wheat is one of the three major cereal crops which feed the human race and the major staple crop in temperate countries
Wheat is a major source of protein in the diets of humans and livestock but we know little about the mechanisms that determine the patterns of protein synthesis in the developing endosperm
We have used a combination of enrichment with 15N glutamine and NanoSIMS imaging to establish that the substrate required for protein synthesis is transported radially from its point of entrance in the endosperm cavity across the starchy endosperm tissues, before becoming concentrated in the cells immediately below the aleurone layer

Summary

Introduction

Wheat is one of the three major cereal crops which feed the human race and the major staple crop in temperate countries. The major storage tissue in the cereal grain is the starchy endosperm, which comprises about 80% starch and about 10% protein This is a highly organized and differentiated tissue, with significant gradients in cell composition, protein that is concentrated in the outer few layers of starchy endosperm cells (called subaleurone cells) in all cereals, including wheat (Tosi et al, 2011) and rice (Ohdaira et al, 2011). These gradients will affect the recovery of protein in fractions produced by grain processing, such as milling of wheat to give white flour and polishing of rice. Both of these processes can result in significant loss of protein from the human diet if the outer layers of the starchy endosperm are removed with the bran

Results

Discussion

Conclusion