A Time-Course Comparative Microarray Analysis of Different Genotypes in Japanese Black Pine (Pinus thunbergii) during Attack By Virulent Nematode (Bursaphelenchus xylophilus) and Avirulent Nematode (B. mucronatus)

We performed large-scale gene expression profiling using NimbleGen Pine GeneChip to study P. thunbergii defense responses to the parasitic nematodes. To understand the difference in the defense responses of resistant and susceptible trees, the development of an infection in resistant and susceptible P. thunbergii by virulent populations of B.xylophilus and avirulent population of B. mucronatus was assayed. This time-course microarray analysis, using 21,061 probe sets, measured transcript abundance during resistant and susceptible trees to virulent and avirulent nematodes. A substantial difference in gene expression has already been present between resistant tree vs virulent nematode and susceptible tree vs virulent nematode at 1 day post infection. Some of the probe sets measuring rapidly decreased transcript levels in resistance tree during virulent nematode represented cytochrome P450 and Cell wall-associated hydrolase as well as Translationally-controlled tumor like protein. On the other hand, PR-gene family probe sets (e.g., PR-1, PR-5, PR-6) measured increased transcript abundance in susceptible tree during virulent nematode. Although the difference in gene expression had been present between resistant and susceptible trees to avirulent nematode until the third day, both trees had shown similar gene expression pattern to avirulent nematode after the seventh day. These results reveal the difference within resistant tree during virulent and avirulent nematodes depends on the quantitative differences in the activated defense genes, and the qualitative difference in the defense responses within susceptible trees during virulent and avirulent nematodes depends on the pathogenic strength of nematode.