Protein palmitoylation, a post-translational protein modification, plays an important role in the regulation of substrate protein stability, protein interactions, and protein localization. It is generally believed that there are two mechanisms of palmitoylation: one by acyl-CoA and the other by protein acyltransferase (PAT). In this study, an MdPAT family member, MdPAT16, was identified and shown to have palmitoyltransferase activity. We found that this gene responded to salt stress and that its expression improved plant salt resistance. MdPAT16 was shown to interact with MdCBL1 and stabilize MdCBL1 protein levels through palmitoylation. MdPAT16 further regulated apple sugar content by stabilizing the MdCIPK13-MdSUT2.2 protein complex. We found that the N-terminal sequence of MdCBL1 contains a palmitoylation site and that the N-terminal deletion of MdCBL1 leads to changes in protein stability and subcellular localization. Finally, exogenous salt stress increased the interaction of MdPAT16 with MdCBL1 and the sugar content in apple. These findings suggest that MdPAT16 functions as a stable means for the palmitoylation of downstream protein. It may be a missing link in the plant salt stress response pathway and have an important impact on fruit quality.

中文翻译：

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苹果棕榈酰转移酶MdPAT16通过MdCBL1-MdCIPK13-MdSUT2.2途径调节糖含量

蛋白质棕榈酰化是一种翻译后蛋白质修饰，在调节底物蛋白质稳定性，蛋白质相互作用和蛋白质定位中起重要作用。通常认为棕榈酰化有两种机理：一种是通过酰基辅酶A，另一种是通过蛋白质酰基转移酶（PAT）。在这项研究中，MdPAT家族成员MdPAT16被鉴定并显示具有棕榈酰转移酶活性。我们发现该基因响应盐胁迫，其表达提高了植物的抗盐性。MdPAT16已显示与MdCBL1相互作用，并通过棕榈酰化作用来稳定MdCBL1蛋白水平。MdPAT16通过稳定MdCIPK13-MdSUT2.2蛋白复合物进一步调节苹果糖含量。我们发现，MdCBL1的N末端序列包含一个棕榈酰化位点，并且MdCBL1的N末端缺失导致蛋白质稳定性和亚细胞定位的改变。最后，外源盐胁迫增加了MdPAT16与MdCBL1的相互作用以及苹果中的糖含量。这些发现表明，MdPAT16充当下游蛋白质棕榈酰化的稳定手段。它可能是植物盐胁迫响应途径中缺少的环节，并且对果实品质有重要影响。