Role of a calcium-binding protein in the saliva of Nephotettix cincticeps in ingestion from the sieve tubes

绿色稻叶蝉在取食过程中会分泌唾液。在本研究中，我们在唾液中发现了一个84 kDa的钙结合蛋白(NcSP84)。NcSP84在初级唾液腺的最大小叶中产生。在暴露于叶蝉的水稻韧皮部汁液中检测到NcSP84，证实NcSP84蛋白已被注入筛管。NcSP84的核苷酸和氨基酸序列与公共数据库中的任何序列都没有同源性。基序搜索预测该蛋白有多个EF-Hand，这是在Ca^&lt；2+&gt；结合蛋白中最常见的基序。正如预测的那样，NcSP84具有钙离子结合活性。纯化的NcSP84与Ca~(2+)和Gt~(2+)结合后的迁移率随CaCl2浓度的增加而降低。这些结果表明，NcSP84可在摄食过程中分泌到筛管中，这可能与针头刺入筛管时流入筛管的钙离子结合。这可能会抑制筛分元件的堵塞，并促进筛管的持续摄入。这是首次在食血管昆虫唾液中发现EF-Hand钙结合蛋白基因克隆。

Green rice leafhoppers (Nephotettix cincticeps) secrete saliva during feeding. In this study, we found an 84 kDa calcium-binding protein (NcSP84) in the saliva. The NcSP84 was produced in the largest lobes in the primary salivary glands. The NcSP84 was detected in the phloem sap of rice exposed to leafhoppers, verifying that the NcSP84 protein was injected into the sieve tubes. The nucleotide and amino acid sequences of NcSP84 did not share homology with any sequences in public databases. Motif search predicted that this protein had multiple EF-hands, the most common motif found in Ca^<2+>-binding proteins. As predicted, NcSP84 exhibited Ca^<2+>-binding activity. The mobility of purified NcSP84 bound to Ca^<2+> declined during SDS-PAGE, depending on the concentration of CaCl_2 present. These results suggest that NcSP84 could be secreted into the sieve tubes during feeding, which might bind Ca^<2+> ions that flow into sieve tubes in response to stylet puncturing. This might suppress sieve-element clogging and facilitate continuous ingestion from sieve tubes. This is the first finding of gene cloning of an EF-hand Ca^<2+>-binding protein in the saliva of a vascular-feeding insect