Abstract
The dominant allergenic components of grass pollen are known by immunologists as group 1 allergens. These constitute a set of closely related proteins from the beta-expansin family and have been shown to have cell wall-loosening activity. Group 1 allergens may facilitate the penetration of pollen tubes through the grass stigma and style. In maize (Zea mays), group 1 allergens are divided into two classes, A and B. We have identified 15 genes encoding group 1 allergens in maize, 11 genes in class A and four genes in class B, as well as seven pseudogenes. The genes in class A can be divided by sequence relatedness into two complexes, whereas the genes in class B constitute a single complex. Most of the genes identified are represented in pollen-specific expressed sequence tag libraries and are under purifying selection, despite the presence of multiple copies that are nearly identical. Group 1 allergen genes are clustered in at least six different genomic locations. The single class B location and one of the class A locations show synteny with the rice (Oryza sativa) regions where orthologous genes are found. Both classes are expressed at high levels in mature pollen but at low levels in immature flowers. The set of genes encoding maize group 1 allergens is more complex than originally anticipated. If this situation is common in grasses, it may account for the large number of protein variants, or group 1 isoallergens, identified previously in turf grass pollen by immunologists.
Highlights
The dominant allergenic components of grass pollen are known by immunologists as group 1 allergens
Due to evidence of variation among cultivars, detailed analysis of maize cDNA sequences was limited to those from libraries obtained from inbred line B73 because they can be directly compared with the available genomic sequences
All of the class B genes and nine of the class A genes are represented in pollen-specific expressed sequence tag (EST) collections
Summary
The dominant allergenic components of grass pollen are known by immunologists as group 1 allergens These constitute a set of closely related proteins from the b-expansin family and have been shown to have cell wall-loosening activity. The set of genes encoding maize group 1 allergens is more complex than originally anticipated If this situation is common in grasses, it may account for the large number of protein variants, or group 1 isoallergens, identified previously in turf grass pollen by immunologists. Group 1 grass pollen allergens are considered part of a superfamily of plant cell wall proteins called expansins. Mature grass pollen contains high amounts of group 1 allergens and it has been suggested that the corresponding genes are probably expressed late in pollen development, coinciding with the accumulation of storage proteins and carbohydrates (Knox and Suphioglu, 1996b). In maize, transcripts for group 1 pollen allergens were detected in very low amounts in uninucleate microspores and subsequently increased greatly after the first pollen mitosis (Broadwater et al, 1993)
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