Two tomato endoglucanases have a function during syncytium development

Globodera rostochiensis, as well as other cyst nematodes, induces formation of a multinucleate feeding site, called syncytium, in host roots. In tomato roots infected with a potato cyst nematode, the syncytium is initiated in the cortex or pericycle. Progressive cell wall dissolution and subsequent fusion of protoplasts of newly incorporated cells lead to syncytium formation. Expansion and development of a syncytium strongly depends on modifications of a cell wall, including its degradation, elongation, thickening, and formation of ingrowths within it in close contact with tracheary elements. Recent reports have demonstrated that during formation of syncytium, numerous genes of plant origin, coding for cell wall-modifying enzymes are up-re-gulated. In this research, we studied a detailed distribution and function of two tomato 1,4-β-endoglucanases in developing feeding sites induced by G. rostochiensis. In situ localization of tomato LeCel7 and LeCel8 transcripts and proteins demonstrated that these enzymes were specifically up-regulated within syncytium and in the cells adjacent to the syncytium. In non-infected roots an expression of LeCel7 and LeCel8 was observed in the root cap and lateral root primordia. Our data confirm that cell wall-modifying enzymes of plant origin have a role in a modification of cell wall within syncytia, and demonstrate that plant endoglucanases are involved in syncytia formation.