Three Novel Rice Genes Closely Related to the ArabidopsisIRX9, IRX9L, and IRX14 Genes and Their Roles in Xylan Biosynthesis

Abstract

Xylan is the second most abundant polysaccharide on Earth, and represents a major component of both dicot wood and the cell walls of grasses. Much knowledge has been gained from studies of xylan biosynthesis in the model plant, Arabidopsis. In particular, the irregular xylem (irx) mutants, named for their collapsed xylem cells, have been essential in gaining a greater understanding of the genes involved in xylan biosynthesis. In contrast, xylan biosynthesis in grass cell walls is poorly understood. We identified three rice genes Os07g49370 (OsIRX9), Os01g48440 (OsIRX9L), and Os06g47340 (OsIRX14), from glycosyltransferase family 43 as putative orthologs to the putative β-1,4-xylan backbone elongating Arabidopsis IRX9, IRX9L, and IRX14 genes, respectively. We demonstrate that the over-expression of the closely related rice genes, in full or partly complement the two well-characterized Arabidopsis irregular xylem (irx) mutants: irx9 and irx14. Complementation was assessed by measuring dwarfed phenotypes, irregular xylem cells in stem cross sections, xylose content of stems, xylosyltransferase (XylT) activity of stems, and stem strength. The expression of OsIRX9 in the irx9 mutant resulted in XylT activity of stems that was over double that of wild type plants, and the stem strength of this line increased to 124% above that of wild type. Taken together, our results suggest that OsIRX9/OsIRX9L, and OsIRX14, have similar functions to the Arabidopsis IRX9 and IRX14 genes, respectively. Furthermore, our expression data indicate that OsIRX9 and OsIRX9L may function in building the xylan backbone in the secondary and primary cell walls, respectively. Our results provide insight into xylan biosynthesis in rice and how expression of a xylan synthesis gene may be modified to increase stem strength.

Transcription profiling identifies candidate genes for secondary cell wall formation and hydroxycinnamoyl-arabinoxylan biosynthesis in the rice internode

“…Although recent studies using Arabidopsis mutants with a defective xylan structure showed that several GT43s and GT47s are specifically involved in the synthesis of the xylan backbone (Brown et al 2007;Lee et al 2010;Oikawa et al 2010;Wu et al 2010;York and O'Neill 2008). Bioinformatics approaches and mutant analyses suggested that several genes in the GT43, 47, and 61 families are potentially involved in AX synthesis (Anders et al 2012;Chiniquy et al 2012Chiniquy et al , 2013Mitchell et al 2007). Mitchell et al (2007) also suggested that the members of the PF02458 family, which is one of the subclades of benzylalcohol O-acetyltransferase (BEAT), anthocyanin O-hydroxycinnamoyltransferase (AHCT), anthranilate N-hydroxycinnamoyl/benzoyltransferase (HCBT), deacetylvindoline 4-O-acetyltransferase (DAT) (BAHD) acyltransferase family, might act as AX hydroxycinnamoyl transferases.…”

Asparagus IRX9, IRX10, and IRX14A Are Components of an Active Xylan Backbone Synthase Complex that Forms in the Golgi Apparatus

“…Among these, AtIRX9 and AtIRX14 (both GT43 family members) and AtIRX10 (GT47), as well as their functionally redundant homologs, are believed to be involved directly in xylan backbone biosynthesis and to form a complex in the GA (Rennie and Scheller 2014). Orthologs of the AtIRX proteins have been identified in many other species, including wheat (Zeng et al, 2010), Populus trichocarpa (Lee et al, 2012b), Physcomitrella patens (Hörnblad et al, 2013), Plantago ovata (Jensen et al, 2013), rice (Oryza sativa; Chen et al, 2013;Chiniquy et al, 2013), Gossypium hirsutum , Neolamarckia cadamba (Zhao et al, 2014), and garden asparagus (Asparagus officinalis; Song et al, 2015). Enzymes involved in xylan backbone biosynthesis as well as side chain decorations, such as the arabinosyltransferases, glucuronosyltransferases, and acetylation enzymes, were recently reviewed by Rennie and Scheller (2014) and Hao and Mohnen (2014).…”

Two Trichome Birefringence-Like Proteins Mediate Xylan Acetylation, Which Is Essential for Leaf Blight Resistance in Rice

“…To verify this finding in planta, we performed Suc density gradient centrifugation and western blotting of fractions prepared from wild-type seedlings. The fractions labeled by anti-OsTBL1/2 antibodies were largely identified by anti-IRX14 antibodies that recognize IRX14, a Golgi-protein involved in xylan biosynthesis in rice (Chiniquy et al, 2013;Lee et al, 2014), suggesting that OsTBL1 and IRX14 are present in the same organelle (Fig. 5C).…”