IRX14 and IRX14-LIKE, Two Glycosyl Transferases Involved in Glucuronoxylan Biosynthesis and Drought Tolerance in Arabidopsis

IRX14 and IRX14-LIKE (IRX14L) are two closely related glycosyl transferases in the glycosyl transferase 43 (GT43) family of Arabidopsis. A T-DNA insertion mutant for IRX14 results in comparatively minor changes, such as irregular xylem, while a mutation for IRX14L results in no changes. However, an irx14 and irx14L double mutant severely affects growth and development, with the dwarf plants failing to produce an inflorescence stem. Plants that are homozygous for IRX14 but heterozygous for IRX14L (irx14 irx14L(+/-)) exhibit an intermediate phenotype, including noticeably smaller leaves, stems, and underdeveloped siliques. Additionally, the T-DNA insertion mutant for IRX14 was found to result in a drought-tolerant phenotype. Carbohydrate analysis of total cell wall extracts revealed a reduction in xylose for the irx14 and irx14 irx14L(+/-) mutants, consistent with a defect in glucuronoxylan biosynthesis. Immunolocalization of xylan with the LM10 antibody revealed a loss of xylan in irx14 mutants and a further reduction in the irx14 irx14L(+/-) mutants. IRX14L likely functions redundantly with IRX14 in glucuronoxylan biosynthesis, with IRX14 having a more important role in the process.