Alternaria species are pathogenic to both humans and plants. In humans, it causes several types of diseases such as hypersensitivity, pneumonitis, bronchial asthma, allergic sinusitis and rhinitis. In plants it infects more than 100 species such as potatoes, tomatoes, sugarbeets, and cucumbers. Alternaria species are found in many parts of the world, mostly in warm and humid regions, where spores of this fungus can be present in the atmosphere throughout the year.
A new study from the Center for Plant Biotechnology and Genomics (UPM-INIA) showed that A. alternata produces Alt a 1 protein, which is known to be a strong allergenic protein, which is associated with chronic asthma. It was also recently described that Alt a 1 protein is involved with the pathogenesis-related plant defense protein (PR5).
The most important factor is that the Alt a 1 protein must be bound to a ligand for infection to happen. This ligand is a flavonoid. Flavonoid compounds are known to play a role in plant defense. They are known as secondary metabolites involved in various processes in the plant cell, such as signaling, plant growth, and reproduction.
When Alternaria germinates the infected plant expresses pathogenesis related proteins and produces free radicals as a defense response. The Alt a 1-protein/ ligand reaches plant parts, changes the pH and the ligand is released. The Alt a 1 blocks some of the plants defense proteins and the ligand removes the plants free radicals, this combination lowers the defense response of the plant and thus infection occurs.
The following scenario explained the link between the plant mechanism and human mechanism. In humans when A. alternata spores get in to the respiratory system, it can reach bronchial epithelium. The mechanism of infection would be molecular responses similar to those found in the plants.
This information can be useful in terms of studying the human respiratory infection process as well as other allergy related issues in humans.
María Garrido-Arandia, Javier Silva-Navas, Carmen Ramírez-Castillejo, Nuria Cubells-Baeza, Cristina Gómez-Casado, Domingo Barber, Juan C. Pozo, Pablo G. Melendi, Luis F. Pacios, Araceli Díaz-Perales. Characterisation of a flavonoid ligand of the fungal protein Alt a 1. Scientific Reports, 2016; 6: 33468 DOI: 10.1038/srep3346812.02.16