Environmental stress influences expression of grass group-1 allergen/beta-expansin in pollen of maize and rice

Grass pollen is among the most common outdoor aeroallergens eliciting pollen allergy throughout the world. Grass group-1 allergen or beta-expansin is recognized as a major pollen allergen, particularly in grass family (Poaceae). Expression of beta-expansin have been shown to be dynamic and can be influenced by environmental stresses. This study aims to evaluate the expression of beta-expansin in crop plants, including maize (Zea mays L., Zm) and rice (Oryza sativa L., Os) under different stress conditions, including drought, salt, and flooding. Rice and maize were treated with either flooding stress, salt stress, or drought stress. After one week of treatments, anthers containing pollen were collected followed by RNA extraction and cDNA synthesis. To evaluate relative expression, qRT-PCR was performed using specific primers for beta-expansin and reference genes. Physiological characteristics of treated and untreated maize and rice, including fresh weight, number of anthers, and number of fluorescences were also recorded. Median test and analysis of variance were used to analyze the relative expression among the experimental groups. For both rice and maize, plant fresh weight, number of anthers, and number of inflorescences decreased significantly under stress conditions. Expression of beta-expansin in pollen of maize showed an apparent decrease in all stress treatments relative to control samples. In contrast, a significant increase of beta-expansin expression was detected in rice pollen under all stress-treated conditions. The highest level of increase, found under flooding condition, was approximately 4 times higher than the expression in untreated controls. Because beta-expansin plays a role in pollen cell wall expansion and pollen shedding, change in expression level of this gene reflects its importance during stress. However, the response is highly dependent on different schemes employed by each plant species. Dynamic expression of the beta-expansin in pollen may have an influence on allergenicity of pollen, but the relevance of beta-expansin transcription level and clinically allergic manifestation has to be assessed in further experiments. Environmental stresses, including flooding, salt and drought stresses, can elicit the change of beta-expansin expression and may affect pollen allergenicity.