College of Grassland Science, Nanjing Agricultural University, Nanjing 210095, China.
Plant Physiol. 2023 Dec 30;194(1):564-577. doi: 10.1093/plphys/kiad527.
Zinc finger proteins (ZFPs) are transcription factors involved in multiple cellular functions. We identified a C2H2 type ZFP (MtZPT2-2) in Medicago truncatula and demonstrated that it localizes to the nucleus and inhibits the transcription of 2 genes encoding high-affinity potassium transporters (MtHKT1;1 and MtHKT1;2). MtZPT2-2 transcripts were detected in stem, leaf, flower, seeds and roots, with the highest level in the xylem and phloem of roots and stems. MtZPT2-2 transcription in leaves was reduced after salt stress. Compared with the wild-type (WT), transgenic lines overexpressing MtZPT2-2 had decreased salt tolerance, while MtZPT2-2-knockout mutants showed increased salt tolerance. MtHKT1;1 and MtHKT1;2 transcripts and Na+ accumulation in shoots and roots, as well as in the xylem of all genotypes of plants, were increased after salt treatment, with higher levels of MtHKT1;1 and MtHKT1;2 transcripts and Na+ accumulation in MtZPT2-2-knockout mutants and lower levels in MtZPT2-2-overexpressing lines compared with the WT. K+ levels showed no significant difference among plant genotypes under salt stress. Moreover, MtZPT2-2 was demonstrated to bind with the promoter of MtHKT1;1 and MtHKT1;2 to inhibit their expression. Antioxidant enzyme activities and the gene transcript levels were accordingly upregulated in response to salt, with higher levels in MtZPT2-2-knockout mutants and lower levels in MtZPT2-2-overexpressing lines compared with WT. The results suggest that MtZPT2-2 regulates salt tolerance negatively through downregulating MtHKT1;1 and MtHKT1;2 expression directly to reduce Na+ unloading from the xylem and regulates antioxidant defense indirectly.
锌指蛋白（ZFPs）是参与多种细胞功能的转录因子。我们在紫花苜蓿中鉴定出一种 C2H2 型 ZFP（MtZPT2-2），并证实它定位于细胞核，抑制编码高亲和力钾转运体（MtHKT1;1 和 MtHKT1;2）的 2 个基因的转录。在茎、叶、花、种子和根中检测到 MtZPT2-2 转录物，在根和茎的木质部和韧皮部中含量最高。盐胁迫后叶片中的 MtZPT2-2 转录减少。与野生型（WT）相比，过表达 MtZPT2-2 的转基因系的耐盐性降低，而 MtZPT2-2 敲除突变体的耐盐性增加。盐处理后，MtHKT1;1 和 MtHKT1;2 转录物和地上部和根部以及所有基因型植物木质部的 Na+积累增加，MtZPT2-2 敲除突变体中的 MtHKT1;1 和 MtHKT1;2 转录物和 Na+积累水平较高，而 MtZPT2-2 过表达系中的水平较低与 WT 相比。盐胁迫下植物基因型之间的 K+水平没有显著差异。此外，证明 MtZPT2-2 与 MtHKT1;1 和 MtHKT1;2 的启动子结合以抑制它们的表达。抗氧化酶活性和基因转录水平相应地上调以响应盐胁迫，MtZPT2-2 敲除突变体中的水平较高，而 MtZPT2-2 过表达系中的水平较低与 WT 相比。结果表明，MtZPT2-2 通过直接下调 MtHKT1;1 和 MtHKT1;2 的表达来减少木质部中 Na+的卸载来负调控耐盐性，并间接调控抗氧化防御。
