PTR2 in Arabidopsis thaliana is negatively regulated by ABI4 and plays a key role in water uptake by seeds, ensuring that imbibed seeds proceed to germination. Peptide transporters (PTRs) transport nitrogen-containing substrates in a proton-dependent manner. Among the six PTRs in Arabidopsis thaliana, the physiological role of the tonoplast-localized, seed embryo abundant PTR2 is unknown. In the present study, a molecular physiological analysis of PTR2 was conducted using ptr2 mutants and PTR2CO complementation lines. Compared with the wild type, the ptr2 mutant showed ca. 6 h delay in testa rupture and consequently endosperm rupture because of 17% lower water content and 10% higher free abscisic acid (ABA) content. Constitutive overexpression of the PTR2 gene under the control of the Cauliflower mosaic virus (CaMV) 35S promoter in ptr2 mutants rescued the mutant phenotypes. After cold stratification, a transient increase in ABA INSENSITIVE4 (ABI4) transcript levels during induction of testa rupture was followed by a similar increase in PTR2 transcript levels, which peaked prior to endosperm rupture. The PTR2 promoter region containing multiple CCAC motifs was recognized by ABI4 in electrophoretic mobility shift assays, and PTR2 expression was repressed by 67% in ABI4 overexpression lines compared with the wild type, suggesting that PTR2 is an immediate downstream target of ABI4. Taken together, the results suggest that ABI4-dependent temporal regulation of PTR2 expression may influence water status during seed germination to promote the post-germinative growth of imbibed seeds.

中文翻译：

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肽转运蛋白 2 (PTR2) 增强了拟南芥早期种子萌发过程中的水分吸收。

拟南芥中的 PTR2 受 ABI4 负调控，在种子吸水过程中起关键作用，确保吸收的种子继续发芽。肽转运蛋白 (PTR) 以质子依赖性方式转运含氮底物。在拟南芥中的六个 PTR 中，液泡膜定位的、种子胚丰富的 PTR2 的生理作用是未知的。在本研究中，使用 ptr2 突变体和 PTR2CO 互补系对 PTR2 进行了分子生理分析。与野生型相比， ptr2 突变体显示约。由于含水量降低 17% 和游离脱落酸 (ABA) 含量升高 10%，睾丸破裂延迟 6 小时，从而导致胚乳破裂。在 ptr2 突变体中花椰菜花叶病毒 (CaMV) 35S 启动子控制下的 PTR2 基因组成型过表达挽救了突变体表型。冷分层后，在诱导种皮破裂期间 ABA INSENSITIVE4 (ABI4) 转录水平的短暂增加之后，PTR2 转录水平也出现类似的增加，在胚乳破裂之前达到峰值。在电泳迁移率变化分析中，ABI4 识别了包含多个 CCAC 基序的 PTR2 启动子区域，与野生型相比，ABI4 过表达系中 PTR2 的表达被抑制了 67%，这表明 PTR2 是 ABI4 的直接下游靶标。综合起来，