Rice (Oryza Sativa L.) Whole Grain Genome-Wide Association Study for Neutral Sugar Content

Background Cell wall matrix polysaccharides are structurally complex and diverse, but our knowledge about their synthesis is limited. The building blocks (monosaccharides) of these polysaccharides have critical role in defining the number and the ultrastructure (size) of rice grains, and therefore would have great influence on seed vigor, yield and quality. Genome-wide association study (GWAS) is a method of choice for fine mapping of QTLs involved in defining plant cell wall structure and modifications. The monosaccharides that contribute to major cell wall matrix polysaccharides in whole grains of 197 rice accessions were quantified using acid hydrolysis and high-performance anion-exchange chromatography with pulsed amperometric detection. A GWAS of calculated monosaccharide content in rice whole grain (RWG) was carried out using 33,812 single-nucleotide polymorphisms (SNPs) to identify corresponding markers in 200 kbp flanking regions.Results In total, 49 significant SNPs contained in 19 genomic regions (QTLs) on eight chromosomes of rice were determined to be associated with monosaccharides content. The candidate genes in QTL regions included the following: arabinose content was associated with α-N-arabinofuranosidase, pectinesterase inhibitor, a glycoside hydrolase (GH) from family 16 (GH16 enzyme); xylose content was associated with ethylene-responsive element-binding protein and a pyruvate kinase; mannose content was associated with a MYB family transcription factor and S-domain receptor-like protein kinase; galactose content was associated with a glycocyltransferase (GT) from family 8 (GT8 enzyme), GRAS family transcription factor, glutathione S-transferase, GH16 and GH17 enzymes; fucose content was associated with a GH16 enzyme, lysine-rich arabinogalactan protein 19 and a receptor protein kinase; and finally rhamnose content was associated with OsFBX41, pectinesterase, COBRA-like protein, and OsSAUR13 (Auxin-responsive SAUR).Conclusion The results of this study should improve our understanding of the genetic basis of the factors that might be involved in the biosynthesis and turnover of major matrix polysaccharides present in RWG. Several QTLs were identified on different chromosomes, all are reported for first. Further, our data provide insight that will be useful in the design of future breeding programs, allowing breeders to use available genetic resources more effectively in meeting global food demand and supply.

Molecular Mechanism of Water Transport Through Cellulose Cell Wall Matrix

In plant living tissue, water can flow across cells by different paths, through cell membranes (transcellular path) and plasmodesmata (symplastic path), or through the continuous cell walls matrix (apoplastic path). The relative contribution of these three paths in living tissue is currently unclear and could vary according to species, tissue developmental stage or physiological conditions. Experiments suggested that apoplastic water movement predominates during transpiration. The objective of this study was to investigate the hydraulic process of cellulose cell wall pathway. The effective pore diameter for water flow through the primary wall matrix is between 2 and 20nm. Inside the cell wall polymer porous, there exist hydrophilic/hydrophobic crystal surfaces based on structure anisotropic. Besides, hydrogen bonding and electrostatic interaction and van der Waals (vdW) dispersion force play an important role in water transport inside the Nano cellulose porous. Therefore, the molecular dynamics simulation was applied to reveal the molecular mechanism of surface boundary effect together with various driving force during water passing through cellulose cell wall matrix Nano channel.

Xylans of Red and Green Algae: What Is Known about Their Structures and How They Are Synthesised?

Xylans with a variety of structures have been characterised in green algae, including chlorophytes (Chlorophyta) and charophytes (in the Streptophyta), and red algae (Rhodophyta). Substituted 1,4-β-d-xylans, similar to those in land plants (embryophytes), occur in the cell wall matrix of advanced orders of charophyte green algae. Small proportions of 1,4-β-d-xylans have also been found in the cell walls of some chlorophyte green algae and red algae but have not been well characterised. 1,3-β-d-Xylans occur as triple helices in microfibrils in the cell walls of chlorophyte algae in the order Bryopsidales and of red algae in the order Bangiales. 1,3;1,4-β-d-Xylans occur in the cell wall matrix of red algae in the orders Palmariales and Nemaliales. In the angiosperm Arabidopsis thaliana, the gene IRX10 encodes a xylan 1,4-β-d-xylosyltranferase (xylan synthase), and, when heterologously expressed, this protein catalysed the production of the backbone of 1,4-β-d-xylans. An orthologous gene from the charophyte green alga Klebsormidium flaccidum, when heterologously expressed, produced a similar protein that was also able to catalyse the production of the backbone of 1,4-β-d-xylans. Indeed, it is considered that land plant xylans evolved from xylans in ancestral charophyte green algae. However, nothing is known about the biosynthesis of the different xylans found in chlorophyte green algae and red algae. There is, thus, an urgent need to identify the genes and enzymes involved.