Abstract
Cucumber (Cucumis sativus L.) is threatened by substantial yield losses due to the south root-knot nematode (Meloidogyne incognita). However, understanding of the molecular mechanisms underlying the process of nematode infection is still limited. In this study, we found that M. incognita infection affected the structure of cells in cucumber roots and treatment of the cytoskeleton inhibitor (cytochalasin D) reduced root-knot nematode (RKN) parasitism. It is known that Actin-Depolymerizing Factor (ADF) affects cell structure, as well as the organization of the cytoskeleton. To address the hypothesis that nematode-induced abnormal cell structures and cytoskeletal rearrangements might be mediated by the ADF genes, we identified and characterized eight cucumber ADF (CsADF) genes. Phylogenetic analysis showed that the cucumber ADF gene family is grouped into four ancient subclasses. Expression analysis revealed that CsADF1, CsADF2-1, CsADF2-2, CsADF2-3 (Subclass I), and CsADF6 (Subclass III) have higher transcript levels than CsADF7-1, CsADF7-2 (Subclass II genes), and CsADF5 (Subclass IV) in roots. Members of subclass I genes (CsADF1, CsADF2-1, CsADF2-2, and CsADF2-3), with the exception of CsADF2-1, exhibited a induction of expression in roots 14 days after their inoculation (DAI) with nematodes. However, the expression of subclass II genes (CsADF7-1 and CsADF7-2) showed no significant change after inoculation. The transcript levels of CsADF6 (Subclass III) showed a specific induction at 21 DAI, while CsADF5 (Subclass IV) was weakly expressed in roots, but was strongly up-regulated as early as 7 DAI. In addition, treatment of roots with cytochalasin D caused an approximately 2-fold down-regulation of the CsADF genes in the treated plants. These results suggest that CsADF gene mediated actin dynamics are associated with structural changes in roots as a consequence of M. incognita infection.
Highlights
Root-knot nematodes (Meloidogyne spp., root-knot nematode (RKN)) are one of the most destructive pathogens of vegetables, even low nematode levels can cause high yield losses (Mukhtar et al, 2013; Liu et al, 2015)
Using A.thaliana Actin-Depolymerizing Factor (ADF) protein sequences, we identified and named eight candidates ADF genes based on a basic local alignment search tool (BLAST) search of the Cucumber Genome Database
The results revealed that the cucumber ADF gene family is grouped phylogenetically into four ancient subclasses supported by the existence of homologous ADF protein sequences from each subclass in the A. thaliana. (Figure 1D)
Summary
Root-knot nematodes (Meloidogyne spp., RKN) are one of the most destructive pathogens of vegetables, even low nematode levels can cause high yield losses (Mukhtar et al, 2013; Liu et al, 2015). The organization of the actin cytoskeleton is significantly altered and permanent rearranged, showing large numbers of thick actin bundles and cables throughout the cell cortex (de Almeida Engler et al, 2004; Clément et al, 2009). These actin cables within giant cells may be required to guide the vesicle trafficking that is needed for extensive plasma membrane and cell wall biogenesis during their isotropic growth (Favery et al, 2004). In response to multiple cellular processes, a range of actin binding proteins (ABPs) can dynamically reorganize and remodele the actin cytoskeleton (Ayscough, 1998; Hussey et al, 2006). The ADF proteins bind G-/F-actin and sever the actin filaments to increase actin turnover (Carlier et al, 1997; Maciver, 1998; Chen et al, 2000; Andrianantoandro and Pollard, 2006; Pavlov et al, 2007)
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