While rain is necessary for plant survival, it also contains bacteria and other pathogens that can harm them. So how do plants protect themselves from this threat?
According to a recent study conducted by Nagoya University researchers and colleagues, when plants are exposed to rain, hair-like structures on the leaf surface known as trichomes perceive the rain as a risk factor for disease transmission and activate their immune system to prevent infections. These findings, published in the journal Nature Communications, could contribute to the development of methods to protect plants from infectious diseases caused by rain.
Plants, like humans and other multicellular organisms, have their own immune system. When plants detect pathogens, they express immune-related genes in order to avoid infection.
Raindrops include pathogens such bacteria, filamentous fungus, and viruses, which can cause plant disease. With this in mind, the researchers theorized that plants could perceive rain as a risk factor for illness and respond in some way to protect themselves from it.
To find out how plants respond to rain, a research team led by Professor Yasuomi Tada and Assistant Professor Mika Nomoto of Nagoya University conducted a study using Arabidopsis thaliana seedlings.
Our findings suggest that we may be able to artificially improve plants’ defensive capabilities against diseases at any time and for any length of time. Using this technology, we could make it possible to activate crops’ immune responses when environmental conditions are harsh enough to possibly cause disease in plants, which could result in stable crop yields.Professor Yasuomi Tada
The researchers began by doing RNA sequencing analysis to determine which genes are expressed in rain-soaked leaves. They found that several major immune-related genes are expressed in response to rain, and that immunosuppressive genes called CAMTAs (calmodulin-binding transcription activators) regulate these genes.
Since CAMTAs are controlled by calcium ions (Ca2+), the team hypothesized that rain serves to increase Ca2+ concentrations in cells. They explored how Ca2+ levels in Arabidopsis leaves alter in response to rain by inserting into the leaves GCaMP3, a gene that fluoresces green when bound to Ca2+. Ca2+ levels surrounding trichomes on leaf surfaces increased when the leaves were exposed to rain.
The result suggested that trichomes sense rain as a risk factor and induce calcium waves (transmission of localized increases in Ca2+ tothe surrounding areas) across the leaf to inactivate the immunosuppressor CAMTA and thereby activate immune-related genes.
To validate this, they repeated the trials with Arabidopsis mutants lacking trichomes, and the results showed that the propagation of calcium waves was hindered in the mutants.
“From these results, we confirmed that trichomes play a role in sensing rain as a risk factor and activating immune responses,” says Professor Tada. “Our findings suggest that we may be able to artificially improve plants’ defensive capabilities against diseases at any time and for any length of time. Using this technology, we could make it possible to activate crops’ immune responses when environmental conditions are harsh enough to possibly cause disease in plants, which could result in stable crop yields.”