Origin And Functional Prediction Of Pollen Allergens In Plants

Pollen allergy has long been a major pandemic health problem for human being.However,the evolutionary events and biological function on pollen allergens in plants remain largely unknown.This dissertation focused on pollen allergens in model plants with emphasis on prediction in model plants,taxonomic distribution of homologues and their origin and evolution.The major findings of this dissertation were listed as follows:1.We report the genome-wide prediction of pollen allergens and their biological function in both dicot model plant Arabidopsis thaliana and monocot model plant rice(Oryza sativa L.subsp.japonica).Totally 145 and 107 pollen allergens were predicted from rice and Arabidopsis respectively,including 22 known pollen allergens.2.The analysis of expression patterns and functional prediction of these pollen allergens suggested that they are putatively involved in stress responses and metabolic processes such as cell wall metabolism during pollen development.Pollen allergens displayed ubiquitous expression were mainly associated with stress responses,oxygen spe-cies metabolism and glycolysis.Pollen allergens exhibited high expression specifically in tricellular and mature pollens and these genes were largely related to cell wall metabolism and organization.3.Through analysis and comparison of protein families of putative pollen allergens,we found that these proteins appeared to be derived from the large protein families and became diversified during the evolution.Supportively,sequence analysis of homologues of putative pollen allergens across 25 plant species from green alga to angiosperms suggested that about 40% putative pollen allergenic proteins existed from the lower plants to higher plants,while other allergens seemed to be generated during the evolution,highlighting the ancient and newly origin of pollen allergens during the evolution.Further evolutionary study suggest that although these allergen coding genes appeared to undergo higher rates of gene duplication,their amino acid sequences have less non-synonymous mutations evidenced by Ka/Ks analysis.Specifically,the rate of gene duplication(including tandem repeat and block repeat)of pollen-expressed genes is about 40% in Arabidopsis and 30% in rice.However,the percentage of gene duplication of putative pollen allergens was markedly higher,60% in Arabidopsis and 49% in rice.In rice,the Ka/Ks rate of allergen genes was around 0.25 and significantly lower than other pollen expressed genes;in Arabidopsis,the values were also at a very low level below 0.2,indicating selection pressure on these genes.4.In order to study further the evolution of pollen allergens,comprehensive observation on the sequence and structure of proteins in two proved allergenic families,expansin and profilin,were performed.The results also implied the crucial role of conserved amino acid residues of these allergens in both molecular function and allergenicity.Collectively,a model explaining how pollen allergens were generated and maintained in plants is proposed.This study provides insight into the phylogenetic and evolutionary scenario of pollen allergens that will be helpful to future characterization and epitope screening of pollen allergens.