Quantification of tomato expansins in nematode feeding sites of cyst and root-knot nematodes

Abstract

Sedentary endoparasitic nematodes induce specific feeding structures in roots of their host plants. The cyst nematode Globodera rostochiensis induces syncytia that are formed by local cell wall degradation, subsequent fusion of the protoplasts and hypertrophy. Root-knot nematodes such as Meloid-ogyne incognita induce galls containing giant cells which differentiate by rapid expansion and nuclear divisions in absence of cytokinesis. Specific cell wall modifications such as expansion, bending and thickening are prominent in both systems. Therefore we investigated gene expression patterns and localization of expansins in a comparative analysis. Expansins are cell wall loosening proteins involved in growth and cell wall disassembly. The expression of expansins in syncytia of G. rostochiensis in tomato and in syncytia and galls induced in Arabidopsis thaliana has already been described. We provide additional information on the expression of 10 tomato expansin isoforms, namely LeEXPA1, -2, -3, -4, -5, -8, -9, -10, -11 and -A18 in 5- and 10-day-old galls of M. incognita with sqRt-Pcr. Further, we determined the quantitative expression of seven differentially regulated tomato expansins in syn-cytia and galls at different developmental stages. We observed a very high induction of LeEXPA2, -5 and -11 with maxima in 10-day-old syncytia and 5-day-old galls. Other members of the gene family were slightly induced in syncytia, whereas in galls only LeEXPA2, -5 and -11 were found to be upregulated. Previous results on the expression of LeEXPA5 in galls are confirmed and detail new information on expansin expression in nematode feeding site is provided. LeEXPA4 and LeEXPA5 have been localized in syncytia recently and we could confirm these results with in situ Rt-Pcr. LeEXPA1, -2, -9, -11 and -18 were also detected in 5- and 10-day-old syncytia and neighboring cells. Especially the expression pattern of LeEXPA2 and LeEXPA5 is of interest, because of their low expression in uninfected roots but their high induction in nematode feeding sites. Our results confirm that expansins are differentially regulated during formation of both syncytia and galls and indicate that these genes are involved in cell wall modifying processes during plant nematode interactions.