Abstract
The complex parasitic strategy of Meloidogyne incognita appears to involve simultaneous expression of its pharyngeal gland-specific effector genes in order to colonize the host plants. Research reports related to effector crosstalk in phytonematodes for successful parasitism of the host tissue is yet underexplored. In view of this, we have used in planta effector screening approach to understand the possible interaction of pioneer genes (msp-18 and msp-20, putatively involved in late and early stage of M. incognita parasitism, respectively) with other unrelated effectors such as cell-wall modifying enzymes (CWMEs) in M. incognita. Host-induced gene silencing (HIGS) strategy was used to generate the transgenic eggplants expressing msp-18 and msp-20, independently. Putative transformants were characterized via qRT-PCR and Southern hybridization assay. SiRNAs specific to msp-18 and msp-20 were also detected in the transformants via Northern hybridization assay. Transgenic expression of the RNAi constructs of msp-18 and msp-20 genes resulted in 43.64–69.68% and 41.74–67.30% reduction in M. incognita multiplication encompassing 6 and 10 events, respectively. Additionally, transcriptional oscillation of CWMEs documented in the penetrating and developing nematodes suggested the possible interaction among CWMEs and pioneer genes. The rapid assimilation of plant-derived carbon by invading nematodes was also demonstrated using 14C isotope probing approach. Our data suggests that HIGS of msp-18 and msp-20, improves nematode resistance in eggplant by affecting the steady-state transcription level of CWME genes in invading nematodes, and safeguard the plant against nematode invasion at very early stage because nematodes may become the recipient of bioactive RNA species during the process of penetration into the plant root.
Highlights
Plant-parasitic root-knot nematode (RKN: Meloidogyne spp.) causes substantial yield losses in various agri- and horticultural crops (Jones et al, 2013; Saucet et al, 2016)
Based on their putative function, abstractly, phytonematode effectors can be categorized into the following divisions: (a) chemotactic factors (HYP and MAP-1 proteins are secreted from amphids, Rosso et al, 2011; Eves-van den Akker et al, 2014) possibly involved in host location and finding suitable feeding sites; (b) cell-wall modifying enzymes (CWMEs) that aid in nematode invasion and migration into and within hosts; (c) host reprogramming modulators associated in the initiation and maintenance of feeding cells; (d) putative host metabolism regulators to provide nutrients to nematodes; and (e) immunosuppressive components to protect nematodes and feeding cells against host innate defense responses (Mantelin et al, 2017)
Transcripts of all the selected CWMEs were considerably upregulated in the early parasitic stages of M. incognita compared to their marked downregulation in young and egg laying females (Supplementary Figure S4)
Summary
Plant-parasitic root-knot nematode (RKN: Meloidogyne spp.) causes substantial yield losses in various agri- and horticultural crops (Jones et al, 2013; Saucet et al, 2016). RKN secretes a repertoire of effector molecules of pharyngeal gland origin in the host-nematode interface via the stylet orifice. These effectors are thought to play essential roles in plant–nematode interaction starting from the host recognition process to softening of plant cell walls in order to facilitate the migration of nematode, selecting a suitable feeding site in vascular cylinder and establishing feeding cells which serves as the potential sink for nutrients that are necessary for nematode development and reproduction (Gheysen and Mitchum, 2011; Hewezi and Baum, 2013). Based on their putative function, abstractly, phytonematode effectors can be categorized into the following divisions: (a) chemotactic factors (HYP and MAP-1 proteins are secreted from amphids, Rosso et al, 2011; Eves-van den Akker et al, 2014) possibly involved in host location and finding suitable feeding sites; (b) cell-wall modifying enzymes (CWMEs) that aid in nematode invasion and migration into and within hosts; (c) host reprogramming modulators associated in the initiation and maintenance of feeding cells; (d) putative host metabolism regulators to provide nutrients to nematodes; and (e) immunosuppressive components to protect nematodes and feeding cells against host innate defense responses (Mantelin et al, 2017)
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