School of Horticulture and Plant Protection, Yangzhou University, Yangzhou, People's Republic of China.
PLoS One. 2021 Jan 12;16(1):e0244714. doi: 10.1371/journal.pone.0244714. eCollection 2021.
Six putative α-galactosidase genes (α-Gals), three acid forms (CsGAL1, CsGAL2, CsGAL3) and three alkaline forms (CsAGA1, CsAGA2, CsAGAL3), were found in the cucumber genome. It is interesting to know the expression pattern and possible function of these α-Gals in the cucumber plant since it is a stachyose-translocating species. In this study, full-length cDNAs of six α-Gals were cloned and heterologously expressed. The result showed that all recombinant proteins revealed acid or alkaline α-Gal activities with different substrate specificities and pH or temperature responding curves, indicating their distinct roles in cucumber plants. Phylogenetic analysis of collected α-Gal amino acid sequences from different plants indicated that the ancestor of both acid and alkaline α-Gals existed before monocots and dicots separated. Generally, six α-Gal genes are universally expressed in different cucumber organs. CsGAL2 highly expressed in fasting-growing leaves, fruits and germinating seeds; CsGAL3 mainly distributes in vacuoles and significantly expressed in cucumber fruits, senescent leaves and seeds during late stage germination; The expression of CsAGA1 increased from leaf 1 to leaf 3 (sink leaves) and then declined from leaf 4 to leaf 7 (source leaves), and this isoform also highly expressed in male flowers and germinating seeds at early stage; CsAGA2 significantly expressed in cucumber leaves and female flowers; CsAGA3 is localized in plastids and also actively expressed in senescent leaves and germinating seeds; The role of CsGAL1 in cucumber plants is now unclear since its expression was relatively low in all organs. According to their expression patterns, subcellular localizations and previously reported functions of these isoforms in other plants, combining the data of soluble sugars contents in different tissues, the possible functions of these α-Gals were discussed.
在黄瓜基因组中发现了六个假定的α-半乳糖苷酶基因（α-Gals），三种酸性形式（CsGAL1、CsGAL2、CsGAL3）和三种碱性形式（CsAGA1、CsAGA2、CsAGAL3）。由于黄瓜是一种棉子糖转运物种，了解这些α-Gals 在黄瓜植物中的表达模式和可能功能是很有趣的。在这项研究中，克隆并异源表达了六个α-Gals 的全长 cDNA。结果表明，所有重组蛋白均显示出酸性或碱性α-Gal 活性，具有不同的底物特异性和 pH 或温度响应曲线，表明它们在黄瓜植物中具有不同的作用。从不同植物中收集的α-Gal 氨基酸序列的系统发育分析表明，酸性和碱性α-Gals 的祖先是在单子叶植物和双子叶植物分化之前存在的。一般来说，六个α-Gal 基因在不同的黄瓜器官中普遍表达。CsGAL2 在快速生长的叶片、果实和萌发种子中高表达；CsGAL3 主要分布在液泡中，在黄瓜果实、衰老叶片和后期萌发种子中显著表达；CsAGA1 的表达从第 1 叶到第 3 叶（汇叶）增加，然后从第 4 叶到第 7 叶（源叶）减少，该同工型也在早期雄性花和萌发种子中高表达；CsAGA2 在黄瓜叶片和雌花中显著表达；CsAGA3 定位于质体，在衰老叶片和萌发种子中也积极表达；由于其在所有器官中的表达相对较低，因此 CsGAL1 在黄瓜植物中的作用目前尚不清楚。根据它们在不同组织中的表达模式、亚细胞定位以及这些同工型在其他植物中的先前报道功能，结合不同组织中可溶性糖含量的数据，讨论了这些α-Gals 的可能功能。
