The cell wall microstructures of syncytia induced by cyst nematodes

Plant parasitic cyst nematodes induce the formation of specialised feeding structures, termed syncytia, from which they feed within the host roots. The multinucleate syncytium initiates from a single host root cell and expands by the local cell wall dissolution of neighbouring cells.
In this study, a set of monoclonal antibodies were applied to reveal the microstructures of syncytial cell walls induced by four economically important cyst nematode species, Globodera pallida, Heterodera glycines, Heterodera avenae and Heterodera filipjevi, in their respective potato, soybean and wheat host roots. In situ fluorescence analysis revealed that cell walls of syncytia induced by G. pallida and H. glycines share high structural similarity. Both consisted of abundant xyloglucans, methyl-esterified homogalacturonan and pectic arabinans. In contrast, the walls of syncytia induced in wheat roots by H. avenae and H. filipjevi contain much less xyloglucan but are rich in feruloylated and substituted heteroxylans and arabinans, with variable levels of mixed-linkage glucans and galactans.
Further investigations were implemented using a range of cell wall related Arabidopsis xyloglucan and pectic arabinan mutants. In situ analysis was applied on those H. schachtii induced syncytia. The results indicated the strong adaptions during the induction and formation of the syncytia while the cell wall composition of the syncytium was stable. Besides, the syncytial wall pectin methyl-esterification status was shown to fluctuate along with the syncytium development in addition to coping with induced PEG-simulated drought stress. Further analysis was carried out on selected pectic homogalacturonan related mutants, and the fluorescence-based quantifications revealed the complexity of the forming and regulating pectin methyl esterification.
Transgenic wheat lines with a root-cap-specific promoter were made via biolistics, in the hope of using this system to further investigate the syncytia formed in wheat, which were shown to be different from the other syncytia analysed.