Cell cycle maneuvering: a strategy taken by plant parasitic nematode to induce specialized feeding sites in plant roots.

Abstract

Plant-parasitic nematodes of the genera Meloidogyne are capable to induce giant cells that undergo repeated mitosis without cytokinesis possibly alternated with endoreduplication cycles. Promoter activity and mRNA localization of key cell cycle genes like CDKA;1, CDKB1;1, CYCB1;1, and CYCA2;1 showed early induction of these genes in both nematode feeding site (NFS). In addition, disturbance in NFS development and nematode maturation were observed during treatment of infected roots with cell cycle inhibitors. DNA synthesis experiments demonstrated that both feeding sites undergo extra endocycles possibly justifying the large nuclei present in NFC. How precisely nematodes manipulate the cell cycle in their favor remains to be understood. A systematic comparison of the temporal and spatial expression pattern of different classes of core cell cycle genes between uninfected roots and nematode infected Arabidopsis thaliana plants resulted in the identification of a collection of genes possibly implicated in NFC development. Among them, one member of the so-called interactors of cyclin-dependent kinase/Kip-related proteins (ICK/KRP), negative regulators of the cell cycle, showed to be upregulated during NFS development. Recent work has shown that KRP2 might regulate mitosis-to-endocycle transition during Arabidopsis leaf development and is highly expressed in endoreduplicating cells as potentially occurring in nematode feeding cells KRPs. To address the direct relevance of these cell cycle inhibitors genes for NFS ontogeny, mutant lines over- expressing and knocking-down are being used to determine how NFS development is affected, and which family members are potential involved in the NFS formation. Furthermore, in vivo subcellular localization of these cell cycle proteins in NFS has been followed to understand the dynamics of these proteins during giant cell development. Based on our preliminary results, some of these cell cycles inhibitors genes are promising candidates involved in NFS development.