Fundación Instituto Leloir and IIBBA-CONICET. Av. Patricias Argentinas 435, Buenos Aires C1405BWE, Argentina.
CONICET, Instituto de Agrobiotecnología del Litoral, Universidad Nacional del Litoral, Colectora Ruta Nacional 168 km 0, 3000, Santa Fe, Argentina.
Plant Physiol. 2023 Dec 30;194(1):81-93. doi: 10.1093/plphys/kiad533.
Plant genomes encode a unique group of papain-type Cysteine EndoPeptidases (CysEPs) containing a KDEL endoplasmic reticulum (ER) retention signal (KDEL-CysEPs or CEPs). CEPs process the cell-wall scaffolding EXTENSIN (EXT) proteins that regulate de novo cell-wall formation and cell expansion. Since CEPs cleave EXTs and EXT-related proteins, acting as cell-wall-weakening agents, they may play a role in cell elongation. The Arabidopsis (Arabidopsis thaliana) genome encodes 3 CEPs (AtCPE1-AtCEP3). Here, we report that the genes encoding these 3 Arabidopsis CEPs are highly expressed in root-hair (RH) cell files. Single mutants have no evident abnormal RH phenotype, but atcep1-3 atcep3-2 and atcep1-3 atcep2-2 double mutants have longer RHs than wild-type (Wt) plants, suggesting that expression of AtCEPs in root trichoblasts restrains polar elongation of the RH. We provide evidence that the transcription factor NAC1 (petunia NAM and Arabidopsis ATAF1, ATAF2, and CUC2) activates AtCEPs expression in roots to limit RH growth. Chromatin immunoprecipitation indicates that NAC1 binds to the promoter of AtCEP1, AtCEP2, and, to a lower extent, AtCEP3 and may directly regulate their expression. Inducible NAC1 overexpression increases AtCEP1 and AtCEP2 transcript levels in roots and leads to reduced RH growth while the loss of function nac1-2 mutation reduces AtCEP1-AtCEP3 gene expression and enhances RH growth. Likewise, expression of a dominant chimeric NAC1-SRDX repressor construct leads to increased RH length. Finally, we show that RH cell walls in the atcep1-3 atcep3-2 double mutant have reduced levels of EXT deposition, suggesting that the defects in RH elongation are linked to alterations in EXT processing and accumulation. Our results support the involvement of AtCEPs in controlling RH polar growth through EXT processing and insolubilization at the cell wall.
植物基因组编码一组独特的木瓜蛋白酶型半胱氨酸内肽酶（CysEPs），它们含有一个 KDEL 内质网（ER）保留信号（KDEL-CysEPs 或 CEP）。CEP 加工细胞壁支架 EXTENSIN（EXT）蛋白，调节新细胞壁的形成和细胞扩张。由于 CEP 切割 EXT 和 EXT 相关蛋白，充当细胞壁弱化剂，它们可能在细胞伸长中发挥作用。拟南芥（Arabidopsis thaliana）基因组编码 3 个 CEP（AtCPE1-AtCEP3）。在这里，我们报告说，编码这 3 个拟南芥 CEP 的基因在根毛（RH）细胞文件中高度表达。单突变体没有明显的异常 RH 表型，但 atcep1-3 atcep3-2 和 atcep1-3 atcep2-2 双突变体的 RH 比野生型（WT）植物长，表明根毛原细胞中 AtCEP 的表达抑制 RH 的极性伸长。我们提供的证据表明，转录因子 NAC1（矮牵牛 NAM 和拟南芥 ATAF1、ATAF2 和 CUC2）激活根中 AtCEPs 的表达，以限制 RH 的生长。染色质免疫沉淀表明，NAC1 结合到 AtCEP1、AtCEP2 的启动子上，在较低程度上结合到 AtCEP3 的启动子上，并可能直接调节它们的表达。诱导型 NAC1 过表达增加了根中 AtCEP1 和 AtCEP2 的转录水平，并导致 RH 生长减少，而功能丧失的 nac1-2 突变降低了 AtCEP1-AtCEP3 基因的表达并增强了 RH 的生长。同样，表达显性嵌合 NAC1-SRDX 阻遏物构建体导致 RH 长度增加。最后，我们表明，在 atcep1-3 atcep3-2 双突变体中，RH 细胞壁的 EXT 沉积水平降低，表明 RH 伸长缺陷与 EXT 加工和积累的改变有关。我们的结果支持 AtCEPs 通过 EXT 加工和细胞壁不溶物参与控制 RH 极性生长。
