Molecular Changes Concomitant with Vascular System Development in Mature Galls Induced by Root-Knot Nematodes in the Model Tree Host Populus tremula × P. alba.

Fabien Baldacci-Cresp,Geert Goeminne,Annegret Kohler,Mondher El Jaziri,Nelly Badalato,Adeline Mol,Kris Morreel,Janice De Almeida Engler,Marie Baucher,Wout Boerjan,Marc Behr

doi:10.3390/ijms21020406

Abstract

One of the most striking features occurring in the root-knot nematode Meloidogyne incognita induced galls is the reorganization of the vascular tissues. During the interaction of the model tree species Populus and M. incognita, a pronounced xylem proliferation was previously described in mature galls. To better characterise changes in expression of genes possibly involved in the induction and the formation of the de novo developed vascular tissues occurring in poplar galls, a comparative transcript profiling of 21-day-old galls versus uninfected root of poplar was performed. Genes coding for transcription factors associated with procambium maintenance and vascular differentiation were shown to be differentially regulated, together with genes partaking in phytohormones biosynthesis and signalling. Specific signatures of transcripts associated to primary cell wall biosynthesis and remodelling, as well as secondary cell wall formation (cellulose, xylan and lignin) were revealed in the galls. Ultimately, we show that molecules derived from the monolignol and salicylic acid pathways and related to secondary cell wall deposition accumulate in mature galls.

Highlights

Phytoparasitic nematodes cause damage to plants thereby leading to substantial yield losses to annual and perennial plants worldwide [1]
All the differentially expressed genes were represented in ClueGO and CluePEDIA [18,19] within Cytoscape using their Arabidopsis thaliana homologs ID (Table S3 and Figure 1)
Among SCW structural genes upregulated in galls (Table S2), we found genes involved in monolignol biosynthesis such as Phe AMMONIA LYASE (PAL) (Potri.016G091100, Potri.006G126800), CINNAMATE 4-HYDROXYLASE (C4H) (Potri.018G146100), CINNAMOYL-CoA REDUCTASE (CCR) (Potri.001G045500), CAFFEOYL-CoA O-METHYLTRANSFERASE (CCoAOMT) (Potri.008G136600, Potri.009G099800) and CINNAMYL ALCOHOL DEHYDROGENASE (CAD) (Potri.016G078300) (Table 2)

Summary

Introduction

Phytoparasitic nematodes cause damage to plants thereby leading to substantial yield losses to annual and perennial plants worldwide [1]. Root-knot nematodes (RKN) (Meloidogyne spp.) are obligate sedentary parasites that enter the root of the plant host at the second juvenile stage. An extensive network of xylem cells enfolding GCs is a typical anatomical feature in galls induced by RKN [2,3]. A drastic development of xylem was evidenced in poplar (Populus tremula × P. alba) galls 21 days after infection (dai) [4]. This profuse vascular system development most likely ensures food for the nematode development and reproduction. Upon completion of the life cycle, the adult nematode female extrudes an egg mass out of the root and once eggs hatch stage 2 juvenile nematodes, subsequent infection cycles will most likely occur in the same root [5]

Methods

Results

Conclusion