ABSTRACT
Plant-parasitic nematodes Meloidogyne spp induce an elaborate permanent feeding site characterized by the redifferentiation of root cells into multinucleate and hypertrophied giant cells. We have isolated by a promoter trap strategy an Arabidopsis thaliana formin gene, AtFH6, which is upregulated during giant cell formation. Formins are actin-nucleating proteins that stimulate de novo polymerization of actin filaments. We show here that three type-I formins were upregulated in giant cells and that the AtFH6 protein was anchored to the plasma membrane and uniformly distributed. Suppression of the budding defect of the Saccharomyces cerevisiae bni1Delta bnr1Delta mutant showed that AtFH6 regulates polarized growth by controlling the assembly of actin cables. Our results suggest that AtFH6 might be involved in the isotropic growth of hypertrophied feeding cells via the reorganization of the actin cytoskeleton. The actin cables would serve as tracks for vesicle trafficking needed for extensive plasma membrane and cell wall biogenesis. Therefore, determining how plant parasitic nematodes modify root cells into giant cells represents an attractive system to identify genes that regulate cell growth and morphogenesis.
Subject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/metabolism , Arabidopsis/parasitology , Membrane Proteins/metabolism , Microfilament Proteins/metabolism , Nematode Infections/metabolism , Tylenchoidea/metabolism , Actins/metabolism , Amino Acid Sequence/genetics , Animals , Arabidopsis/genetics , Arabidopsis Proteins/genetics , Arabidopsis Proteins/isolation & purification , Base Sequence/genetics , Cell Membrane/genetics , Cell Membrane/metabolism , Cell Wall/genetics , Cell Wall/metabolism , DNA, Complementary/analysis , DNA, Complementary/genetics , Formins , Gene Expression Regulation, Plant/genetics , Glucuronidase/metabolism , Host-Parasite Interactions/genetics , Membrane Proteins/genetics , Membrane Proteins/isolation & purification , Microfilament Proteins/genetics , Microfilament Proteins/isolation & purification , Molecular Sequence Data , Mutation/genetics , Nematode Infections/genetics , Phylogeny , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae/metabolism , Transport Vesicles/genetics , Transport Vesicles/metabolism , Up-Regulation/geneticsABSTRACT
Phytohormones as well as temporal and spatial regulation of the cell cycle play a key role in plant development. Here, we investigated the function and regulation of an alfalfa (Medicago sativa) A2-type cyclin in three distinct root developmental programs: in primary and secondary root development, nodule development, and nematode-elicited gall formation. Using transgenic plants carrying the Medsa;cycA2;2 promoter-beta-glucuronidase gene fusion, in combination with other techniques, cycA2;2 expression was localized in meristems and proliferating cells in the lateral root and nodule primordia. Rapid induction of cycA2;2 by Nod factors demonstrated that this gene is implicated in cell cycle activation of differentiated cells developing to nodule primordia. Surprisingly, cycA2;2 was repressed in the endoreduplicating, division-arrested cells both during nodule development and formation of giant cells in nematode-induced galls, indicating that CycA2;2 was dispensable for S-phase in endoreduplication cycles. Overexpression of cycA2;2 in transgenic plants corresponded to wild type protein levels and had no apparent phenotype. In contrast, antisense expression of cycA2;2 halted regeneration of somatic embryos, suggesting a role for CycA2;2 in the formation or activity of apical meristems. Expression of cycA2;2 was up-regulated by auxins, as expected from the presence of auxin response elements in the promoter. Moreover, auxin also affected the spatial expression pattern of this cyclin by shifting the cycA2;2 expression from the phloem to the xylem poles.
