Table 2_Transcriptomic insights into arabinogalactan protein mechanism of action in galactosyltransferase octuple mutants.docx

Arabinogalactan-proteins (AGPs) are a family of hyperglycosylated hydroxyproline-rich glycoproteins essential for plant growth and development and generally contain 10% protein and 90% carbohydrate. Eight galactosyltransferases (GALTs), specifically GALT2-GALT9, catalyze galactose addition to hydroxyproline residues in the AGP protein backbone and initiate glycosylation of AGPs. Arabidopsis galt octuple mutants that result from the knockout of eight GALT genes displayed severe phenotypic changes, prompting our exploration of the mechanisms of action of AGPs by comparing the transcripts of galt octuple mutant flowers and siliques to wild type flowers and siliques in Arabidopsis thaliana. Transcriptomic analysis of flowers from galt octuple mutants revealed 930 significantly differentially expressed genes (426 upregulated, 504 downregulated). Many of the downregulated genes are reported to be crucial for pollen tube growth, pollination, and flower development. In siliques, there were 1,476 significantly differentially expressed genes (1,027 upregulated, 449 downregulated), including the downregulation of genes for pectin methyl esterase inhibitors (PMEIs) and suspensor development. There were 45 genes commonly downregulated in flowers and siliques, which are reportedly crucial for glycosylation, glycoprotein synthesis, and cell wall modification. On the other hand, there were 194 commonly upregulated genes linked to calcium ion binding with kinases and phosphatases in the signal transduction pathways, cell-cell communication, stress response and pathogen defense response regulation in both flowers and siliques. These findings offer insights into plant molecular responses to AGP dynamics and provide a foundation for further investigations into the underlying mechanisms of action of AGPs by revealing the genes and pathways related to AGP function, suggesting that AGPs may mediate the effects of these genes or pathways, in part, by influencing signal transduction pathways involving kinases and phosphatases.

阿拉伯半乳糖蛋白（Arabinogalactan-proteins, AGPs）是一类富含羟脯氨酸的高糖基化糖蛋白，对植物生长发育至关重要，其组分通常包含10%的蛋白质与90%的碳水化合物。目前已发现8种半乳糖基转移酶（galactosyltransferases, GALTs），具体为GALT2至GALT9，可催化半乳糖连接至AGP蛋白骨架的羟脯氨酸残基，从而启动AGP的糖基化修饰。通过敲除拟南芥（Arabidopsis thaliana）的8种GALT基因获得的galt八突变体呈现出显著的表型变化，这促使我们开展AGP作用机制的相关研究：对比该八突变体与野生型拟南芥的花和角果的转录组。对galt八突变体花组织的转录组分析显示，共鉴定到930个显著差异表达基因，其中426个上调表达、504个下调表达。其中大量下调基因据报道与花粉管生长、授粉及花发育密切相关。在角果组织中，共鉴定到1476个显著差异表达基因，其中1027个上调表达、449个下调表达，包括果胶甲酯酶抑制剂（pectin methyl esterase inhibitors, PMEIs）编码基因与胚柄发育相关基因的下调。在花与角果组织中，共有45个基因呈现共同下调趋势，这些基因据报道对糖基化、糖蛋白合成及细胞壁修饰具有关键作用。与之相对，在两类组织中共有194个基因共同上调，这些基因涉及信号转导通路中的激酶与磷酸酶介导的钙离子结合、细胞间通讯、应激响应及病原菌防御应答调控等过程。本研究通过揭示与AGP功能相关的基因及通路，为解析植物对AGP动态变化的分子响应机制提供了新视角，也为进一步探究AGP的潜在作用机制奠定了基础；研究结果表明，AGPs或可通过影响涉及激酶与磷酸酶的信号转导通路，部分介导上述基因或通路的生物学功能。