Wheat contains abundant xylan in cell walls of all tissues, but in endosperm, there is an unusual form of xylan substituted only by arabinose (arabinoxylan; AX) that has long chains and low levels of feruloylation, a fraction of which is extractable in water (WE‐AX). WE‐AX acts as soluble dietary fibre but also gives rise to viscous extracts from grain, a detrimental trait for some non‐food uses of wheat. Here, we show that a glycosyl transferase family 43 wheat gene abundantly expressed in endosperm complements the Arabidopsis irx9 mutant and so name the three homoeologous genes TaIRX9b. We generated wheat lines with a constitutive knockout of TaIRX9b by stacking loss‐of‐function alleles for these homeologues from a mutagenized hexaploid wheat population resulting in decreases in grain extract viscosity of 50%–80%. The amount and chain length of WE‐AX molecules from grain of these triple‐stack lines was decreased accounting for the changes in extract viscosity. Imaging of immature wheat grain sections of triple‐stacks showed abolition of immunolabelling in endosperm with LM11 antibody that recognizes epitopes in AX, but also showed apparently normal cell size and shape in all cell types, including endosperm. We identified differentially expressed genes from endosperm of triple‐stacks suggesting that compensatory changes occur to maintain this endosperm cell wall integrity. Consistent with this, we observed increased ferulate dimerization and increased cross‐linking of WE‐AX molecules in triple‐stacks. These novel wheat lines lacking functional TaIRX9b therefore provide insight into control of wheat endosperm cell walls.

中文翻译：

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小麦中TaIRX9b基因功能的丧失会降低链长和籽粒中阿拉伯木聚糖的含量，但会增加交联。

小麦在所有组织的细胞壁中都含有丰富的木聚糖，但是在胚乳中，有一种不寻常的木聚糖形式，仅被阿拉伯糖（arabinoxylan; AX）取代，具有长链和低水平的阿魏酸酯化，其中一部分可在水中提取（ WE‐AX）。WE‐AX充当可溶性膳食纤维，但也会从谷物中产生粘性提取物，这对小麦的某些非食品用途来说是有害的。在这里，我们显示在胚乳中大量表达的糖基转移酶家族43小麦基因与拟南芥irx9互补突变体，因此命名为三个同源基因TaIRX9b。通过堆叠诱变的六倍体小麦群体中这些同源基因的功能缺失等位基因，我们构建了具有TaIRX9b组成型敲除功能的小麦品系，导致籽粒提取物粘度降低了50％–80％。这些三重堆积系的谷物中WE-AX分子的数量和链长减少了，这是提取液粘度变化的原因。对三叠堆未成熟小麦籽粒切片的成像显示，胚乳中的免疫标记被LM11抗体取消了，该抗体可识别AX中的表位，但在所有类型的细胞中（包括胚乳）也显示出正常的细胞大小和形状。我们从三重胚乳的胚乳中鉴定出差异表达的基因，表明发生了代偿性变化以维持胚乳细胞壁的完整性。与此相一致，我们观察到阿魏二聚体的增加和三叠堆中WE-AX分子的交联增加。因此，这些缺乏功能性TaIRX9b的新型小麦品系为控制小麦胚乳细胞壁提供了见识。