National Engineering Laboratory for Crop Molecular Breeding, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
Plant Physiol. 2023 May 31;192(2):1569-1583. doi: 10.1093/plphys/kiad135.
Although microRNA408 (miR408) is a highly conserved miRNA, the miR408 response to salt stress differs among plant species. Here, we show that miR408 transcripts are strongly repressed by salt stress and methyl viologen treatment in maize (Zea mays). Application of N, N1-dimethylthiourea partly relieved the NaCl-induced down-regulation of miR408. Transgenic maize overexpressing MIR408b is hypersensitive to salt stress. Overexpression of MIR408b enhanced the rate of net Na+ efflux, caused Na+ to locate in the inter-cellular space, reduced lignin accumulation, and reduced the number of cells in vascular bundles under salt stress. We further demonstrated that miR408 targets ZmLACCASE9 (ZmLAC9). Knockout of MIR408a or MIR408b or overexpression of ZmLAC9 increased the accumulation of lignin, thickened the walls of pavement cells, and improved salt tolerance of maize. Transcriptome profiles of the wild-type and MIR408b-overexpressing transgenic maize with or without salt stress indicated that miR408 negatively regulates the expression of cell wall biogenesis genes under salt conditions. These results indicate that miR408 negatively regulates salt tolerance by regulating secondary cell wall development in maize.
尽管 microRNA408（miR408）是一种高度保守的 miRNA，但不同植物物种对盐胁迫的 miR408 响应存在差异。在这里，我们表明 miR408 转录物在玉米（Zea mays）中受到盐胁迫和甲基紫精处理的强烈抑制。应用 N，N1-二甲基硫脲部分缓解了 NaCl 诱导的 miR408 下调。过表达 MIR408b 的转基因玉米对盐胁迫敏感。MIR408b 的过表达增强了净 Na+外排的速率，导致 Na+位于细胞间隙，减少了木质素的积累，并减少了盐胁迫下维管束中的细胞数量。我们进一步证明 miR408 靶向 ZmLACCASE9（ZmLAC9）。MIR408a 或 MIR408b 的敲除或 ZmLAC9 的过表达增加了木质素的积累，使 pavement 细胞的壁变厚，并提高了玉米的耐盐性。有或没有盐胁迫的野生型和 MIR408b 过表达转基因玉米的转录组谱表明，miR408 在盐条件下负调控细胞壁生物发生基因的表达。这些结果表明，miR408 通过调节玉米次生细胞壁的发育来负调控盐耐受性。
