Pathogenicity of fungus in plants could provide clinical information about respiratory diseases

Researchers from UPM id reveal how mould from humidity caused by rotting fruits and vegetables unfolds a surprising strategy to infect plants.

A team of researchers from Centre for Plant Biotechnology and Genomics (CBGP, UPM-INIA), has published the results on "Alt a 1" in an article released in Scientific Reports from the Nature group. "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 are 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 been remained largely unexplored until now.

In order to understand these processes, researchers from Biotecnología Vegetal group at CBGP (UPM-INIA) studied these processes at 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 accumulate in the spores, the protein is released in the presence of moisture. However, it does 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 internet about common respiratory disorders (such as allergic sinusitis, rhinitis, pneumonitis and bronchial asthma) and other allergies caused by these fungi.