Wu Ai-Min, Rihouey Christophe, Seveno Martial, Hörnblad Emma, Singh Sunil Kumar, Matsunaga Toshiro, Ishii Tadashi, Lerouge Patrice, Marchant Alan
Department of Forest Genetics and Plant Physiology, SLU, SE-901 83 Umeå, Sweden.
Plant J. 2009 Feb;57(4):718-31. doi: 10.1111/j.1365-313X.2008.03724.x. Epub 2008 Oct 16.
Arabidopsis IRX10 and IRX10-LIKE (IRX10-L) proteins are closely related members of the GT47 glycosyltransferase family. Single gene knock-outs of IRX10 or IRX10-L result in plants with either a weak or no mutant phenotype. However irx10 irx10-L double mutants are severely affected in their development, with a reduced rosette size and infrequent formation of a small infertile inflorescence. Plants homozygous for irx10 and heterozygous for irx10-L have an intermediate phenotype exhibiting a short inflorescence compared with the wild type, and an almost complete loss of fertility. Stem sections of the irx10 homozygous irx10-L heterozygous or irx10 irx10-L double mutants show decreased secondary cell-wall formation. NMR analysis shows that signals derived from the reducing end structure of glucuronoxylan were detected in the irx10 single mutant, and in the irx10 homozygous irx10-L heterozygous combination, but that the degree of polymerization of the xylan backbone was reduced compared with the wild type. Additionally, xylans from irx10 stem tissues have an almost complete loss of the GlcUA side chain, whereas the level of 4-O-Me-GlcUA was similar to that in wild type. Deletion of the predicted signal peptide from the N terminus of IRX10 or IRX10-L results in an inability to rescue the irx10 irx10-L double mutant phenotype. These findings demonstrate that IRX10 and IRX10-L perform a critical function in the synthesis of glucuronoxylan during secondary cell-wall formation, and that this activity is associated with the formation of the xylan backbone structure. This contrasts with the proposed function of the tobacco NpGUT1, which is closely related to the Arabidopsis IRX10 and IRX10-L proteins, in rhamnogalacturonan II biosynthesis.
拟南芥IRX10和类IRX10（IRX10-L）蛋白是GT47糖基转移酶家族中关系密切的成员。IRX10或IRX10-L的单基因敲除会导致植株出现弱突变表型或无突变表型。然而，irx10 irx10-L双突变体在发育过程中受到严重影响，莲座叶大小减小，很少形成小的不育花序。irx10纯合且irx10-L杂合的植株具有中间表型，与野生型相比，其花序较短，且育性几乎完全丧失。irx10纯合、irx10-L杂合或irx10 irx10-L双突变体的茎段显示次生细胞壁形成减少。核磁共振分析表明，在irx10单突变体以及irx10纯合、irx10-L杂合组合中检测到了源自葡糖醛酸木聚糖还原端结构的信号，但与野生型相比，木聚糖主链的聚合度降低。此外，irx10茎组织中的木聚糖几乎完全丧失了GlcUA侧链，而4-O-Me-GlcUA的水平与野生型相似。从IRX10或IRX10-L的N端删除预测的信号肽会导致无法挽救irx10 irx10-L双突变体表型。这些发现表明，IRX10和IRX10-L在次生细胞壁形成过程中葡糖醛酸木聚糖的合成中发挥关键作用，并且这种活性与木聚糖主链结构的形成有关。这与烟草NpGUT1（与拟南芥IRX10和IRX10-L蛋白密切相关）在鼠李糖半乳糖醛酸聚糖II生物合成中所提出的功能形成对比。
