Graduate School of Science and Technology, Division of Biological Science, Nara Institute of Science and Technology, Ikoma 630-0192, Japan.
Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8562, Japan.
Plant Cell. 2024 Sep 3;36(9):3298-3317. doi: 10.1093/plcell/koae221.
Xylem vessels function in the long-distance conduction of water in land plants. The NAC transcription factor VASCULAR-RELATED NAC-DOMAIN7 (VND7) is a master regulator of xylem vessel cell differentiation in Arabidopsis (Arabidopsis thaliana). We previously isolated suppressor of ectopic xylem vessel cell differentiation induced by VND7 (seiv) mutants. Here, we report that the responsible genes for seiv3, seiv4, seiv6, and seiv9 are protein ubiquitination-related genes encoding PLANT U-BOX46 (PUB46), an uncharacterized F-BOX protein (FBX), PUB36, and UBIQUITIN-SPECIFIC PROTEASE1 (UBP1), respectively. We also found decreased expression of genes downstream of VND7 and abnormal xylem transport activity in the seiv mutants. Upon VND7 induction, ubiquitination levels from 492 and 180 protein groups were upregulated and downregulated, respectively. VND7 induction resulted in the ubiquitination of proteins for cell wall biosynthesis and protein transport, whereas such active protein ubiquitination did not occur in the seiv mutants. We detected the ubiquitination of three lysine residues in VND7: K94, K105, and K260. Substituting K94 with arginine significantly decreased the transactivation activity of VND7, suggesting that the ubiquitination of K94 is crucial for regulating VND7 activity. Our findings highlight the crucial roles of target protein ubiquitination in regulating xylem vessel activity.
木质部导管在陆地植物的远距离导水过程中发挥作用。NAC 转录因子 VASCULAR-RELATED NAC-DOMAIN7（VND7）是拟南芥木质部导管细胞分化的主要调节因子。我们之前分离了 VND7 诱导的异位木质部导管细胞分化的抑制子（seiv）突变体。在这里，我们报告 seiv3、seiv4、seiv6 和 seiv9 的相关基因分别编码蛋白泛素化相关基因 PLANT U-BOX46（PUB46）、一个未被描述的 F-BOX 蛋白（FBX）、PUB36 和泛素特异性蛋白酶 1（UBP1）。我们还发现 seiv 突变体中 VND7 下游基因的表达下调和异常木质部运输活性。在 VND7 诱导下，分别有 492 和 180 个蛋白质组的泛素化水平上调和下调。VND7 诱导导致细胞壁生物合成和蛋白质运输相关蛋白的泛素化，而在 seiv 突变体中则没有发生这种活性蛋白的泛素化。我们检测到 VND7 中三个赖氨酸残基的泛素化：K94、K105 和 K260。用精氨酸取代 K94 显著降低了 VND7 的转录激活活性，表明 K94 的泛素化对于调节 VND7 活性至关重要。我们的研究结果强调了靶蛋白泛素化在调节木质部导管活性中的关键作用。
