Ectopic expression of Kip‐related proteins restrains root‐knot nematode‐feeding site expansion

Abstract

SummaryThe development of nematode feeding sites induced by root-knot nematodes involves the synchronized activation of cell cycle processes such as acytokinetic mitoses and DNA amplification. A number of key cell cycle genes are reported to be critical for nematode feeding site development. However, it remains unknown whether plant cyclin-dependent kinase (CDK) inhibitors such as the Arabidopsis interactor/inhibitor of CDK (ICK)/Kip-related protein (KRP) family are involved in nematode feeding site development. This study demonstrates the involvement of Arabidopsis ICK2/KRP2 and ICK1/KRP1 in the control of mitosis to endoreduplication in galls induced by the root-knot nematode Meloidogyne incognita.Using ICK/KRP promoter-GUS fusions and mRNA in situ hybridizations, we showed that ICK2/KRP2, ICK3/KRP5 and ICK4/KRP6 are expressed in galls after nematode infection. Loss-of-function mutants have minor effects on gall development and nematode reproduction. Conversely, overexpression of both ICK1/KRP1 and ICK2/KRP2 impaired mitosis in giant cells and blocked neighboring cell proliferation, resulting in a drastic reduction of gall size.Studying the dynamics of protein expression demonstrated that protein levels of ICK2/ KRP2 are tightly regulated during giant cell development and reliant on the presence of the nematode.This work demonstrates that impeding cell cycle progression by means of ICK1/KRP1 and ICK2/KRP2 overexpression severely restricts gall development, leading to a marked limitation of root-knot nematode development and reduced numbers of offspring.

Enhanced levels of plant cell cycle inhibitors hamper root-knot nematode-induced feeding site development

“…11,15 Recently, we initiated a detailed functional analyses of the Arabidopsis KRP gene family during RKN [Meloidogyne incognita (Kofoid and White, 1919) Chitwood, 1949] infection, in order to reveal their potential involvement on this plant-pathogen interaction. 16,17 Of the 7 Arabidopsis genes, we observed that 3 members of this family (KRP2, KRP5, and KRP6 ) were highly expressed during at least a certain time span of nematode feeding root-knot nematodes (rKn) are highly specialized, obligatory plant parasites. these animals reprogram root cells to form large, multinucleate, and metabolically active feeding cells (giant cells) that provide a continuous nutrient supply during 3-6 weeks of the nematode's life.…”

“…Despite the accelerated mitotic activity in gall tissues, development of the associated nematodes seems unchanged and these physiological alterations display no synergetic effect to RKN reproduction. 17 …”

“…Gall tissue undergo intense cell cycle activity, therefore, inhibition of cell cycle progression in the nematode feeding sites seems to have a more drastic effect compared with uninfected plant cells. 2,16,17 Recently, we have shown that overexpression of KRP4 resulted in an aberrant segregation of nuclear DNA, promoting a delay in nematode feeding site development. 16 The variability of nucleus phenotype of the different KRPs challenged with RKN (KRP1, KRP2, and KRP4) may reflect diverse functions or different effects on CDK/CYCs activity.…”

“…We also studied the effect of KRP loss-of-function in single (KRP2 −/− ) and double (KRP2 −/− KRP6 −/− ) mutant lines, as well as in multi-silenced RNAi lines for 7 KRP genes, 17 during nematode infection. Mutation or attenuation of KRP genes resulted in ectopic activation of mitosis in RKN feeding-sites as illustrated by an increased number of nuclei in giant cells, and abnormal proliferation of vascular cells surrounding these giant cells.…”

“…1D and F), and almost devoid of neighboring cells, seems to significantly affect nematode development. 17 Although all KRPs are capable to inhibit CDKA/CYC complexes in plant cells, 24 their mode of action can be differentially modulated in galls induced by RKN. Gall tissue undergo intense cell cycle activity, therefore, inhibition of cell cycle progression in the nematode feeding sites seems to have a more drastic effect compared with uninfected plant cells.…”