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SPECIAL SESSION: Host-pathogen interactions at the plant surface

The first line of defense - cell walls in plant immunity
Gerit Bethke - University of Minnesota Twin Cities.

Plant cell walls are both early barriers to pathogen entry and a source for signaling molecules that induce immune signaling. We have previously reported that pectin content and methyl esterification status affect plant immunity. Plants with mutations in UDP-Glucuronate-4-Epimerase 1 (GAE1) and GAE6 plants have strongly reduced homogalacturonan content and show increased susceptibility to the fungus Botrytis cinerea isolate Gallo 1. Other groups have described plants with mutations in a glycosyltransferase (QUA1), a methyltransferase (QUA2) or CGR2 and CGR3 that affect pectin methyl esterification that show reduced pectin content and growth defects. To further study the effects of pectin on plant growth and immunity we first compared pectin content in all mutants in parallel. Uronic acid content and binding of the homogalacturon-specific LM 20 antibody was strongly reduced in gae1-1 gae6-1, gae1-2 gae6-2 and cgr2 cgr3 and somewhat reduced in qua2. In contrast to the observed increased susceptibility of gae1 gae6 to B. cinerea Gallo 1, cgr2 cgr3 and qua2 plants showed increased resistance to this pathogen. In cgr2 cgr3 heightened resistance coincided with constitutively increased expression of the immune marker genes PR1, PAD3 and JAZ10 and reduced expression of PDF1.2 whereas expression of these genes was unaltered in qua2. Additionally, qua2, cgr2 cgr3 and gae1-2 gae6-2 plants showed increased water loss of detached rosette leaves. These genotypes also showed decreased ABA-induced stomatal closure. Our data suggest that different changes in pectin abundance and modification affect plant immunity in specific ways.