Researchers from Universidad Politécnica de Madrid (UPM) reveal how mold from humidity caused by rotting fruits and vegetables unfolds a surprising strategy to infect plants.
A team of researchers from the Centre for Plant Biotechnology and Genomics (CBGP, UPM-INIA), has published the results on “Alt a 1.” “Alt a 1” is a strongly allergenic protein found in certain endophytic fungi species that causes severe asthma.
This study provides better understanding of the role played by this protein in the pathogenicity of the fungus. Besides, the mechanism identified in plants can also provide information of clinical interest about respiratory diseases and allergies caused by these fungal.
Spores of certain Alternaria fungus that appear as mold in plants of most of our crops are present in the atmosphere throughout the year. “Alt a 1” is a strongly allergenic protein present in the spores of Alternaria alternata before germination. “Alt a 1” is responsible for infections and common respiratory conditions and is also considered as the major allergen associated with chronic asthma.
The pathogenic action of this protein is linked to the production of certain toxic compounds and the increasing production of reactive oxygen species by plants which are toxic agents that cause the cell death. "Alt a 1" interacts with defense proteins that plants express when attacked by inhibiting their activity. The Alternaria spores remain on the surface of the plant without inducing symptoms while waiting for the right moment to germinate. When this occurs, the spores provoke a cascade of processes that had remained largely unexplored until now.
In order to understand these processes, researchers from Biotecnología Vegetal group at CBGP (UPM-INIA) studied these processes at the molecular scale. In addition to revealing details of the infection in plants, the molecular responses to the presence of "Alt a 1" could provide clues about the answers associated to the development of allergies and other human disorders.
Results reveal that "Alt 1" acts with a compound (a ligand) which is the main actor in the infection. After accumulating in the spores, the protein is released in the presence of moisture. However, it does this along with its ligand: a derivative of quercetin and a member of a family of secondary compounds widespread in plants, flavonoids, also present in fruits and vegetables.
The following scenario for the versatility of "Alt a 1" is proposed. When Alternaria species germinates, the infected plant expresses pathogenesis-related proteins and produces free radicals as a defense response. "Alt a 1" is released mainly as a tetramer carrying its flavonol ligand. When the Alt a 1-ligand complex reaches other plant compartments, the pH changes and the ligand is released.
Then, the combined action of "Alt a 1" -blocking certain defense proteins- and ligand -removing the free radicals- disarms the defense responses of the plant and eases the infection. Likewise, if the Alternaria alternata spores are in the air, a person can inhale them and reach the bronchial epithelium. In its way towards eventual immune system responses, "Alt a 1" must go through regions of changing acidity, thus the break of its aggregates and release of the ligand would trigger molecular responses analogous to the ones found in the plant.
This mechanism that has been identified in plants can provide clinical information of great interest about common respiratory disorders (such as allergic sinusitis, rhinitis, pneumonitis, and bronchial asthma) and other allergies caused by these fungi.
Illustration: Tomato after 5 days of infection by Alternaria alternata. Credit: María Garrido Arandia, CBGP, UPM, Lab 151.
Universidad Politécnica de Madrid News Release (10/14/16)
Science Daily (10/14/16)
Abstract (Characterisation of a flavonoid ligand of the fungal protein Alt a 1. Scientific Reports; 2016, 6: 33468.)