Spatial Distribution of Selected Chemical Cell Wall Components in the Embryogenic Callus of Brachypodium distachyon.

Alexander Betekhtin,Robert Hasterok,Magdalena Rojek,Ewa Kurczynska,Anna Milewska-Hendel,Robert Gawecki,Jagna Karcz,Randall P Niedz

doi:10.1371/journal.pone.0167426

Abstract

Brachypodium distachyon L. Beauv. (Brachypodium) is a species that has become an excellent model system for gaining a better understanding of various areas of grass biology and improving plant breeding. Although there are some studies of an in vitro Brachypodium culture including somatic embryogenesis, detailed knowledge of the composition of the main cell wall components in the embryogenic callus in this species is missing. Therefore, using the immunocytochemical approach, we targeted 17 different antigens of which five were against the arabinogalactan proteins (AGP), three were against extensins, six recognised pectic epitopes and two recognised hemicelluloses. These studies were complemented by histological and scanning electron microscopy (SEM) analyses. We revealed that the characteristic cell wall components of Brachypodium embryogenic calli are AGP epitopes that are recognised by the JIM16 and LM2 antibodies, an extensin epitope that is recognised by the JIM11 antibody and a pectic epitopes that is recognised by the LM6 antibody. Furthermore, we demonstrated that AGPs and pectins are the components of the extracellular matrix network in Brachypodium embryogenic culture. Additionally, SEM analysis demonstrated the presence of an extracellular matrix on the surface of the calli cells. In conclusion, the chemical compositions of the cell walls and ECMSN of Brachypodium callus show spatial differences that correlate with the embryogenic character of the cells. Thus, the distribution of pectins, AGPs and hemicelluloses can be used as molecular markers of embryogenic cells. The presented data extends the knowledge about the chemical composition of the embryogenic callus cells of Brachypodium.

Highlights

IntroductionDue to its introduction beyond its natural range, populations of this species have been observed in North and South America, Australia and Western Europe [1]
The embryogenic calli were represented by two distinct categories, one of which was vitreous and friable (Fig 1B; white asterisks), while the other was a compact callus that was represented by embryogenic masses that were yellowish in colour (Fig 1B; yellow asterisks)
Embryogenesis of the callus can be induced from meristematic cells, and from differentiated cells that have originated from leaf, stem or root tissues

Summary

Introduction

Due to its introduction beyond its natural range, populations of this species have been observed in North and South America, Australia and Western Europe [1]. Brachypodium is closely related to many temperate zone key cereals, such as wheat, barley, rye and oats as well as forage grasses. It has many useful biological traits, for example a small nuclear genome, small stature, rapid life cycle, the ability to self-pollinate and simple growth requirements, which along with the diverse germplasm resources and well-developed research infrastructure make this species an excellent model system for both a better understanding of grass biology and improving plant breeding, including the faster domestication of emerging crops [2, 3]. The main fields of research on Brachypodium have been extensively reviewed in [4]

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Results

Conclusion