Cell Wall Proteome of Wheat Grain Endosperm and Outer Layers at Two Key Stages of Early Development.

Cherkaoui Mehdi,Geairon Audrey,Lollier Virginie,Rogniaux Hélène,Jamet Elisabeth,Bouder Axelle,Francin-Allami Mathilde,Guillon Fabienne,Larré Colette

doi:10.3390/ijms21010239

Abstract

The cell wall is an important compartment in grain cells that fulfills both structural and functional roles. It has a dynamic structure that is constantly modified during development and in response to biotic and abiotic stresses. Non-structural cell wall proteins (CWPs) are key players in the remodeling of the cell wall during events that punctuate the plant life. Here, a subcellular and quantitative proteomic approach was carried out to identify CWPs possibly involved in changes in cell wall metabolism at two key stages of wheat grain development: the end of the cellularization step and the beginning of storage accumulation. Endosperm and outer layers of wheat grain were analyzed separately as they have different origins (maternal and seed) and functions in grains. Altogether, 734 proteins with predicted signal peptides were identified (CWPs). Functional annotation of CWPs pointed out a large number of proteins potentially involved in cell wall polysaccharide remodeling. In the grain outer layers, numerous proteins involved in cutin formation or lignin polymerization were found, while an unexpected abundance of proteins annotated as plant invertase/pectin methyl esterase inhibitors were identified in the endosperm. In addition, numerous CWPs were accumulating in the endosperm at the grain filling stage, thus revealing strong metabolic activities in the cell wall during endosperm cell differentiation, while protein accumulation was more intense at the earlier stage of development in outer layers. Altogether, our work gives important information on cell wall metabolism during early grain development in both parts of the grain, namely the endosperm and outer layers. The wheat cell wall proteome is the largest cell wall proteome of a monocot species found so far.

Highlights

The wheat grain is a caryopsis composed of an embryo separated from the starchy endosperm and aleurone cells by the scutellum
Transcriptomic data on the developing wheat grain allowed for the identification of glycosyl hydrolases (GHs) genes [15], and recently, we reported the first data on the cell wall proteome of endosperm and the outer layers of wheat grain at a given developmental stage [34]
Our quantitative proteomic work provides an overview of cell wall proteins (CWPs) of early-developing grains of wheat, both in the endosperm and the outer layers

Summary

Introduction

The wheat grain is a caryopsis composed of an embryo separated from the starchy endosperm and aleurone cells by the scutellum. The progeny is surrounded by the maternal tissues, which are composed of several outer layers [1]. They consist of the pericarp, the testa, and the nucellar epidermis [2]. The pericarp includes epidermal cells, parenchyma cells, and cross and tube cells. Cytological and physiological features of wheat endosperm and pericarp were characterized all along the grain development [3,4,5]. By around 150 growing degree days (GDD), the layers of the outer integument are the first to degenerate, whereas endosperm cells continue to divide.

Methods

Findings

Discussion

Conclusion