ABSCISIC ACID INSENSITIVE5 (ABI5) is an important regulator of abscisic acid (ABA) signaling pathway involved in regulating seed germination and postgerminative growth in Arabidopsis, which integrates various phytohormone pathways to balance plant growth and stress responses. However, the transcriptional regulatory mechanisms underlying ABI5 and its interacting proteins remain largely unknown. Here, we found that inhibition of AtTOR could increase ABA content by up-regulating the expression levels of ABA biosynthesis-related genes, and thus activated the expression of ABA-responsive genes. Pharmacological assay showed that abi5-1 mutant was insensitive to TOR inhibitor AZD8055, whereas AtABI5 overexpression lines were hypersensitive to AZD8055 in Arabidopsis. Biochemical interaction assays demonstrated that ABI5 physically interacted with the RIBOSOMAL S6 KINASE2 (S6K2) protein in plant cell. S6K2 positively regulated ABA responses during seedling growth and upregulated ABA-responsive genes expression. Furthermore, genetic and physiological analysis indicated that AtS6K2 overexpression lines enhanced resistance to drought treatment while AtS6K2 interference lines were sensitive to drought. These results indicated that AtABI5 interacted with AtS6K2 to positively modulate ABA responses during seedling growth and shed light on a underlying mechanism of the crosstalk between TOR and ABA signaling pathways in modulating seedling growth in Arabidopsis.

脱落酸（ABICISIC ACID INSENSITIVE5）（ABI5）是脱落酸（ABA）信号传导途径的重要调节剂，参与调控种子的萌发和发芽后生长。 拟南芥，它整合了各种植物激素途径，以平衡植物的生长和胁迫响应。但是，ABI5及其相互作用蛋白的转录调控机制仍然未知。在这里，我们发现抑制AtTOR可以通过上调ABA生物合成相关基因的表达水平来增加ABA含量，从而激活ABA响应基因的表达。药理分析表明abi5-1 突变体对TOR抑制剂AZD8055不敏感，而 AtABI5 过表达细胞对AZD8055过敏 拟南芥。生化相互作用测定表明，ABI5与植物细胞中的RIBOSOMAL S6 KINASE2（S6K2）蛋白发生物理相互作用。S6K2积极调节幼苗生长过程中的ABA反应和上调ABA反应基因的表达。此外，遗传和生理分析表明AtS6K2 过表达系增强了对干旱处理的抵抗力，而 AtS6K2干扰线对干旱敏感。这些结果表明，AtABI5与AtS6K2相互作用以积极调节幼苗生长过程中的ABA反应，并揭示了TOR和ABA信号通路之间的串扰调节幼苗生长的潜在机制。拟南芥。