Deficiency of water and phosphate induce lignin deposition in roots. LACCASEs, a family of cell wall-localized multicopper oxidases, are involved in lignin biosynthesis. We demonstrate here that LACCASE2 (LAC2) acts as a negative regulator of lignin deposition in root vascular tissues during water deficit. An Arabidopsis (Arabidopsis thaliana) transfer DNA insertion mutant of LAC2 displayed a short primary root and high lignin deposition in root vascular tissues. However, restoration of LAC2 expression rescued these phenotypes. LAC2 expression was significantly down-regulated under water deficit and posttranscriptionally regulated by microRNA397b (miR397b) in roots under normal and water-deficit conditions. Down-regulation of miR397b activity increased LAC2 expression and root length, and decreased lignin content in root vasculature. Similarly, phosphate (Pi) deficiency inversely affected miR397b and LAC2 expression. Lignin deposition in the root elongation zone under Pi-limited conditions was dependent on LAC2 expression. Localized iron accumulation and callose deposition in the root elongation zone under Pi deficiency increased with LAC2-dependent lignification, suggesting a direct relationship between these processes. Our study reveals a regulatory role for the miR397b-LAC2 module in root lignification during water and phosphate deficiency.

中文翻译：

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MicroRNA397b -LACCASE2模块调节水和磷酸盐缺乏时的根木质素化。

缺水和磷酸盐会导致木质素在根部沉积。LACCASEs是细胞壁定位的多铜氧化酶的一个家族，参与木质素的生物合成。我们在这里证明LACCASE2（LAC2）在缺水期间充当木质素在根血管组织中沉积的负调节剂。LAC2的拟南芥（Arabidopsis thaliana）转移DNA插入突变体在根部维管组织中显示出短的初生根和高木质素沉积。但是，LAC2表达的恢复挽救了这些表型。在正常和缺水情况下，根系中的LAC2表达在缺水时显着下调，并由microRNA397b（miR397b）转录后调控。miR397b活性的下调增加了LAC2的表达和根的长度，并降低了根脉管系统中木质素的含量。同样，磷酸（Pi）缺乏症反过来影响miR397b和LAC2表达。在Pi限制条件下，木质素在根伸长区的沉积取决于LAC2表达。Pi缺乏下根伸长区的局部铁积累和call质沉积随LAC2依赖性木质化的增加而增加，表明这些过程之间存在直接关系。我们的研究揭示了miR397b-LAC2模块在缺水和缺磷期间在根木质化中的调节作用。暗示这些过程之间存在直接关系。我们的研究揭示了miR397b-LAC2模块在缺水和缺磷期间在根木质化中的调节作用。暗示这些过程之间存在直接关系。我们的研究揭示了miR397b-LAC2模块在缺水和缺磷期间在根木质化中的调节作用。