Multiple C2 domains and transmembrane region proteins (MCTPs) may act as transport mediators of other regulators. Although increased number of MCTPs in higher plants implies their diverse and specific functions in plant growth and development, only a few plant MCTPs have been studied and no study on the MCTPs in cotton has been reported. In this study, we identified 31 MCTPs in G. hirsutum, which were classified into five subfamilies according to the phylogenetic analysis. GhMCTPs from subfamily V exhibited isoelectric points (pIs) less than 7, whereas GhMCTPs from subfamily I, II, III and IV exhibited pIs more than 7.5, implying their distinct biological functions. In addition, GhMCTPs within subfamily III, IV and V exhibited more diverse physicochemical properties, domain architectures and expression patterns than GhMCTPs within subfamily I and II, suggesting that GhMCTPs within subfamily III, IV and V diverged to perform more diverse and specific functions. Analyses of conserved motifs and pIs indicated that the N-terminus was more divergent than the C-terminus and GhMCTPs’ functional divergence might be mainly contributed by the N-terminus. Furthermore, yeast two-hybrid assay indicated that the N-terminus was responsible to interact with target proteins. Phylogenetic analysis classified multiple N-terminal C2 domains into four subclades, suggesting that these C2 domains performed different molecular functions in mediating the transport of target proteins. Our systematic characterization of MCTPs in G. hirsutum will provide helpful information to further research GhMCTPs’ molecular roles in mediating other regulators’ transport to coordinate growth and development of various cotton tissues.

中文翻译：

---

全基因组鉴定和表征陆地棉中多个C2域和跨膜区蛋白。

多个C2域和跨膜区蛋白（MCTP）可能充当其他调节子的转运介质。尽管高等植物中MCTP数量的增加暗示了它们在植物生长和发育中的多样性和特殊功能，但仅对少数几种植物MCTP进行了研究，但尚未报道棉花中MCTP的研究。在这项研究中，我们确定了G. hirsutum中的31个MCTP，根据系统发育分析将其分为5个亚科。来自子家族V的GhMCTPs的等电点（pIs）小于7，而来自子家族I，II，III和IV的GhMCTPs的pIs大于7.5，表明它们的独特生物学功能。此外，子家族III，IV和V中的GhMCTP表现出更多样化的理化特性，域结构和表达模式比亚家族I和II中的GhMCTPs高，这表明亚家族III，IV和V中的GhMCTPs分化以执行更多样化和更具体的功能。对保守基序和pI的分析表明，N末端比C末端更趋异，GhMCTPs的功能差异可能主要由N末端引起。此外，酵母双杂交试验表明N末端负责与靶蛋白相互作用。系统发育分析将多个N末端C2域划分为四个子小节，表明这些C2域在介导目标蛋白的运输中具有不同的分子功能。我们对G中MCTP的系统表征。