Seminars with Chapple and Guillon

Dr Fabienne Guillon:
CELL WALLS OF MATERNAL TISSUES IN THE DEVELOPING WHEAT GRAIN

Dr Fabienne Guillon

Abstract: The wheat grain maternal tissues comprise several specialized cell layers. These layers fulfill many functions including nutriment supply and protection. In the dry grain, the maternal layers ‘stick’ to the aleurone layer of the endosperm and it has been suggested that they may play a role in the control of endosperm growth. Outer layers in wheat grain are also decisive for wheat end-use properties.
The cell wall composition of the outer layers in the developing wheat grain was characterized using biochemistry, microspectroscopy and immunocytochemistry approaches. Their composition differs from the composition of endosperm cell walls and substantial variations were observed between the different outer cell layers. Complex patterns of polysaccharide deposition and remodelling were uncovered. For instance results showed that cell walls from the seed coat are particular with an abundant and specific deposition of glucuronoxylans and low-methylated pectin. Lignins are present in low amount in the outer pericarp and unexpectedly lignin monomers were detected quite early during grain filling. Subcellular proteomics conducted on the different tissues of the grain unveiled many proteins potentially involved in cell wall formation and remodelling. Several cell wall related GTs and GHs were found both in outer layers and starchy endosperm e.g. GT2 CslF6 implicated in (1-3)(1-6)-b-D-glucans synthesis, while others were found specifically in the outer layers ex : IRX14 homolog and GUX homolog.
This raises many questions concerning properties and functions of these cell walls.

This project receives funding from the Research National Agency in the framework of the BREEDWHEAT project.

Dr Fabienne Guillon is Research Director. She received her Ph.D. degree in Food science in 1987 from the University of Nantes (France). She is a research scientist at INRA since 1989 and is currently working at the Research Unit Biopolymers, Intercations, Assemblies (Nantes, France). She has several years of experience in the area of dietary fiber and gastrointestinal function. Her research is now focused on structure and composition of plant cell-wall and how cell wall architecture might influence the end-use properties of plant material . She is the authors of about 70  peer-reviewed international publications.  

Dr Clint Chapple:
INTERPLAY BETWEEN REGULATION OF LIGNIN BIOSYNTHESIS, GLUCOSINOLATES AND ANTHOCYANINS

Dr Clint Chapple

Abstract: The products of the phenylpropanoid pathway range from complex, insoluble polymers such as lignin and suberin, to soluble flavonoids and hydroxycinnamate esters, to volatile compounds used to attract pollinators. In addition to its important role in plant biology, lignin has a significant impact on the effectiveness of converting cell wall polysaccharides to ethanol or second-generation biofuels. For this reason, a great deal of research has focused on altering phenylpropanoid metabolism through mutation or RNAi-mediated down-regulation of genes encoding pathway enzymes. Although many of these manipulations lead to significant alterations in plant metabolism, defects at a number of biosynthetic steps lead to a common suite of pleiotropic phenotypes such as dwarfing and sterility, the severity of which is dependent on the strength of the metabolic restriction.
We identified several semi-dominant mutants which contain lower levels of soluble phenylpropanoids including lignin and carry point mutations in the previously uncharacterized gene At2g48110. These mutants are also dwarfed and have a pale seed coat. As in several other mutants we have characterized, the decreased levels of the phenylpropanoid-derived UV protectant sinapoylmalate results in a reduced epidermal fluorescence (ref) phenotype, and we have named this mutant ref4. We have obtained multiple lines of additional supporting evidence that the REF4 protein play a role in the suppression of phenylpropanoid biosynthesis in wild-type plants.
REF4 and its paralog, REF4-related 1 (RFR1), have recently been shown to be components of Mediator, a large multi-protein complex that facilitates interactions between DNA-bound transcription factors and RNA polymerase II. Mutants of Arabidopsis that lack REF4 and RFR1 hyperaccumulate phenylpropoanoids, are viable and show little in the way of developmental changes. Surprisingly, ref4/rfr1 mutations mitigate the dwarf phenotype and sterility of the ref8 mutant of Arabidopsis which is defective in the early phenylpropanoid pathway enzyme p-coumaroyl shikimate 3-hydroxylase. Our data reveal that dwarfism in at least some phenylpropanoid pathway mutants is the result of a cascade of transcriptional misregulation that is dependent on Mediator.

Clint Chapple, Department of Biochemistry, Purdue University, 175 South University Street, West Lafayette, IN, USA, 47907-2063;