Exploiting cell cycle inhibitor genes of the KRP family to control root‐knot nematode induced feeding sites in plants

Abstract

Cell cycle control in galls provoked by root-knot nematodes involves the activity of inhibitor genes like the Arabidopsis ICK/KRP members. Ectopic KRP1, KRP2 and KRP4 expression resulted in decreased gall size by inhibiting mitotic activity, whereas KRP6 induces mitosis in galls. Herein, we investigate the role of KRP3, KRP5 and KRP7 during gall development and compared their role with previously studied members of this class of cell cycle inhibitors. Overexpression of KRP3 and KRP7 culminated in undersized giant cells, with KRP3 galls presenting peculiar elongated giant cells. Nuclei in KRP3 and KRP5 lines presented a convoluted and apparently connected phenotype. This appearance may be associated with the punctuated protein nuclear localization driven by specific common motifs. As well, ectopic expression of KRP3 and KRP5 affected nematode development and offspring. Decreased mitotic activity in galls of KRP3 and KRP7 lines led to a reduced gall size which presented distinct shapes - from more elongated like in the KRP3 line to small rounded like in the KRP7 line. Results presented strongly support the idea that induced expression of cell cycle inhibitors such as KRP3 and KRP7 in galls can be envisaged as a conceivable strategy for nematode feeding site control in crop species attacked by phytopathogenic nematodes.

The plant WEE1 kinase is involved in checkpoint control activation in nematode‐induced galls

“…Seedlings were grown vertically, allowing roots to stay on the surface, under 16 h : 8 h, 21°C : 18°C light : dark conditions. Each seedling was then infected with 100 surface‐sterilized (Coelho et al., ) and freshly hatched Meloidogyne incognita juveniles, and galls of infected roots were harvested for several tests as described in the following sections.…”

Plant Cyclin-Dependent Kinase Inhibitors of the KRP Family: Potent Inhibitors of Root-Knot Nematode Feeding Sites in Plant Roots

“…This suggests that a level of cell cycle regulation must be triggered in order to control GC formation. During gall maturation (>14DAI), only KRP2 and KRP5 showed a significant transcription activity in GC implying their role in the endoreduplication cycle at this stage of gall development ( Vieira et al, 2013 , 2014 ; Coelho et al, 2017 ). Conversely, the remaining KRP1 , KRP3 , KRP4 and KRP7 genes were not expressed in the galls at any time point during nematode infection.…”

“…Promoter activity as well as expression analysis of the seven Arabidopsis KRP genes ( KRP1 to KRP7 ) have been examined in detail in uninfected roots and during several stages of gall development ( Vieira et al, 2012 , 2013 , 2014 ; Coelho et al, 2017 ). Our data illustrated that three out of the seven members of the KRP gene family, namely KRP2 , KRP5 and KRP6 , are expressed in RKN induced galls and present during a specific time span of the NFS development ( Table 1 ).…”

“…On the other hand, GFP-KRP2, GFP-KRP6, KRP7-GFP proteins became dispersed into the cytoplasm after nuclear envelope break down during mitosis presenting no apparent co-localization to the chromosomes. These proteins will later uniformly re-accumulate in the nuclei of the two newly formed daughter cells ( Vieira et al, 2013 , 2014 ; Coelho et al, 2017 ).…”

“…In the case of KRP5, in vivo examination of RKN-infected roots treated with the proteasome inhibitor MG132, showed enhanced GFP-KRP5 accumulation in the GC nuclei suggesting that KRP5 protein levels are potentially controlled by degradation of the 26S proteasome protein ( Coelho et al, 2017 ). Our observations indicated that KRP5 accompanied the process of GC maturation, and this might be important for cell cycle regulation during the NFS expansion ( Coelho et al, 2017 ). KRP5 has been found to be preferentially expressed in endoreduplicating cells during etiolation and is considered a positive regulator of endoreduplication ( Jégu et al, 2013 ).…”