Johny Jibin, Nihad Mohammad, Alharbi Hattan A, AlSaleh Mohammed Ali, Antony Binu
Department of Plant Protection, Center for Chemical Ecology and Functional Genomics, College of Food and Agricultural Sciences, King Saud University, 11451, Riyadh, Saudi Arabia.
Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czechia.
Sci Rep. 2024 Jul 17;14(1):16541. doi: 10.1038/s41598-024-67309-x.
The red palm weevil (RPW), Rhynchophorus ferrugineus (Olivier), also known as the Asian palm weevil, is an invasive pest that causes widespread damage to palm trees around the globe. As pheromone communication is crucial for their mass attack and survival on palm trees, the olfactory concept of pest control strategies has been widely explored recently. We aim to understand the molecular basis of olfaction in RPW by studying one of the key olfactory proteins in insect pheromone communication, sensory neuron membrane proteins (SNMPs). SNMPs belong to the CD36 (cluster of differentiation 36) family that perform two distinct olfactory roles in insects, either in pheromone (odorant) transfer to the odorant receptors (SNMP1) or in the pheromone clearing process (SNMP2). In this study, we performed antennal transcriptomic screening and identified six SNMPs, mapping them on the R. ferrugineus genome, and confirmed four distinct SNMPs. Both SNMP1 proteins in RPW, viz., RferSNMPu1 and RferSNMPu2, were mapped onto the same scaffold in different loci in the RPW genome. To further understand the function of these proteins, we first classified them using phylogenetic analysis and checked their tissue-specific expression patterns. Further, we measured the relative transcript abundance of SNMPs in laboratory-reared, field-collected adults and pheromone-exposure experiments, ultimately identifying RferSNMPu1 as a potential candidate for functional analysis. We mapped RferSNMPu1 expression in the antennae and found that expression patterns were similar in both sexes. We used RNAi-based gene silencing to knockdown RferSNMPu1 and tested the changes in the RPW responses to aggregation pheromone compounds, 4-methyl-5-nonanol (ferrugineol) and 4-methyl-5-nonanone (ferrugineone), and a kairomone, ethyl acetate using electroantennogram (EAG) recordings. We found a significant reduction in the EAG recordings in the RferSNMPu1 knockdown strain of adult RPWs, confirming its potential role in pheromone detection. The structural modelling revealed the key domains in the RferSNMPu1 structure, which could likely be involved in pheromone detection based on the identified ectodomain tunnels. Our studies on RferSNMPu1 with a putative role in pheromone detection provide valuable insight into understanding the olfaction in R. ferrugineus as well as in other Curculionids, as SNMPs are under-explored in terms of its functional role in insect olfaction. Most importantly, RferSNMPu1 can be used as a potential target for the olfactory communication disruption in the R. ferrugineus control strategies.
红棕象甲（RPW），即锈色棕榈象（Rhynchophorus ferrugineus (Olivier)），也被称为亚洲棕榈象甲，是一种入侵性害虫，在全球范围内对棕榈树造成广泛破坏。由于信息素通讯对于它们在棕榈树上的大规模攻击和生存至关重要，害虫控制策略的嗅觉概念最近得到了广泛探索。我们旨在通过研究昆虫信息素通讯中的一种关键嗅觉蛋白——感觉神经元膜蛋白（SNMPs），来了解红棕象甲嗅觉的分子基础。SNMPs属于CD36（分化簇36）家族，在昆虫中发挥两种不同的嗅觉作用，要么在将信息素（气味剂）传递给气味受体（SNMP1）方面，要么在信息素清除过程（SNMP2）中。在本研究中，我们进行了触角转录组筛选，鉴定出六个SNMPs，并将它们定位在锈色棕榈象的基因组上，确认了四个不同的SNMPs。红棕象甲中的两种SNMP1蛋白，即RferSNMPu1和RferSNMPu2，被定位在锈色棕榈象基因组中不同位点的同一支架上。为了进一步了解这些蛋白的功能，我们首先通过系统发育分析对它们进行分类，并检查它们的组织特异性表达模式。此外，我们测量了实验室饲养、野外采集的成虫以及信息素暴露实验中SNMPs的相对转录丰度，最终确定RferSNMPu1为功能分析的潜在候选对象。我们绘制了RferSNMPu1在触角中的表达图谱，发现两性中的表达模式相似。我们使用基于RNA干扰的基因沉默技术来敲低RferSNMPu1，并通过触角电位（EAG）记录测试红棕象甲对聚集信息素化合物4-甲基-5-壬醇（锈色棕榈象醇）和4-甲基-5-壬酮（锈色棕榈象酮）以及一种利它素乙酸乙酯的反应变化。我们发现成年红棕象甲RferSNMPu1敲低品系的EAG记录显著降低，证实了其在信息素检测中的潜在作用。结构建模揭示了RferSNMPu1结构中的关键结构域，基于所确定的胞外结构域通道，这些结构域可能参与信息素检测。我们对在信息素检测中具有推定作用的RferSNMPu1的研究，为理解锈色棕榈象以及其他象甲科昆虫的嗅觉提供了有价值的见解，因为SNMPs在昆虫嗅觉中的功能作用尚未得到充分探索。最重要的是，RferSNMPu1可作为锈色棕榈象控制策略中嗅觉通讯干扰的潜在靶点。
