Poster: Cell Walls

Abs # 1259: Group 2 and group 3 allergens of grass pollen have plant cell wall-loosening activity characteristic of b-expansins

Presenter:	Li, Lian-Chao , LXL23@PSU.EDU
Authors	Li, Lian-Chao  (A)   Shieh, Mark W. (A)   Cosgrove, Daniel J. (A)
Affiliations:	(A): Pennsylvania State University

Expansins are cell wall-loosening proteins that induce rapid extension and stress relaxation of plant cell walls in a characteristic and unique manner. Group 2 and group 3 allergens from grass pollen are small (~11-kD) proteins with sequence similarity to expansin domain 2, especially to domain 2 of the b-expansin subclass known as group-1 grass pollen allergens. Expansin domain 2 was hypothesized to be a polysaccharide binding domain. We found that native Lol p 3, a group-3 allergen of ryegrass (Lolium perenne) pollen, has significant expansin-like cell wall loosening activity, as does native Phl p 2, a group 2 pollen allergen of timothy grass (Phleum pratense). Recombinant Lol p 3 expressed in E. coli also has cell wall-loosening activity. Cell wall extension induced by Lol p 3 is saturable, has an acidic pH optimum of pH 5 – 5.5, and has high specificity of action for grass cell walls over dicot cell walls. Lol p 3 also acts synergistically to enhance the cell wall-loosening activity of the b-expansin Lol p 1, the group 1 pollen allergen from ryegrass. Analysis of sequence databases indicates that group 2/3 allergens and their homologs are restricted to the grasses, where expression is largely restricted to pollen. These small proteins may aid pollen tube penetration of the stigma and style by softening the cell walls of these maternal tissues. Our results imply that at least part of the characteristic cell wall-loosening action of expansin is attributable to domain 2.