Identification and Expression Analysis of Aquaporins in the Potato Psyllid, Bactericera cockerelli

Aquaporin (AQPs) proteins transport water and uncharged low molecular-weight solutes across biological membranes. Six to 8 AQP genes have been identified in many insect species, but presently only three aquaporins have been characterized in phloem feeding insects. The objective of this study was to identify candidate AQPs in the potato psyllid, Bactericera cockerelli. Herein, we identified four candidate aquaporin cDNAs in B. cockerelli transcriptome. Phylogenetic analysis showed that candidate BcAQP2-like had high similarity to PRIP aquaporins; while candidates BcAQP4-like, BcAQP5-like and BcAQP9-like clustered within clade B. In particular, candidates BcAQP4-like and BcAQP5-like clustered with functionally validated insect aquaglyceroporin proteins. Expression analyses using RT-qPCR showed that all candidates were expressed in all life stages and tissues. Candidates BcAQP4-like and BcAQP5-like were highly expressed in bacteriocytes, while BcAQP9-like appeared to be expressed at high levels in whole body but not in the assayed tissues. This study is the first global attempt to identify putative aquaporins in a phloem feeding insect.水通道蛋白（Aquaporin, AQPs）能够介导水分与不带电荷的低分子量溶质跨生物膜进行转运。目前已有多种昆虫被鉴定出6至8个AQP基因，但截至目前仅在韧皮部取食昆虫中完成了3种水通道蛋白的功能表征。本研究旨在鉴定马铃薯木虱（Bactericera cockerelli）中的候选AQP基因。本研究中，我们从该虫的转录组中鉴定出4条水通道蛋白候选cDNA序列。系统发育分析结果显示，候选蛋白BcAQP2-like与PRIP型水通道蛋白具有较高同源性；而BcAQP4-like、BcAQP5-like及BcAQP9-like则聚集于进化支B内。尤为关键的是，BcAQP4-like与BcAQP5-like与经功能验证的昆虫水甘油通道蛋白（aquaglyceroporin）聚为同一分支。采用实时定量逆转录PCR（RT-qPCR）开展的表达谱分析显示，所有候选AQP基因均在各生命阶段及组织中有所表达。BcAQP4-like与BcAQP5-like在含菌细胞中呈高表达模式，而BcAQP9-like则在全虫体中表达量较高，但在所检测的组织中未呈现显著高表达。本研究为首次在韧皮部取食昆虫中系统性鉴定推定水通道蛋白的探索性工作。