How Plants Activate their Immune Systems in Rain to Fight Dangerous Pathogens

While rain is necessary for plant survival, it also contains bacteria and other pathogens that can harm them. So, how do plants defend themselves against 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 recognise the rain as a risk factor for disease transmission and activate their immune system to prevent infections.

These findings, which were published in the journal Nature Communications, may help to develop methods to protect plants from infectious diseases caused by rain.

Findings of Research:

Plants, like humans and other multicellular organisms, have their own immune systems. When plants detect pathogens, they express immune-related genes in order to avoid infection. Raindrops contain pathogens like bacteria, filamentous fungi, and viruses, which can cause plant disease. With this in mind, the researchers hypothesized that plants could recognize rain as a risk factor for disease and respond in some way to protect themselves from it.

A research team led by Professor Yasuomi Tada and Assistant Professor Mika Nomoto of Nagoya University used Arabidopsis thaliana seedlings to investigate how plants respond to rain. The researchers began by performing RNA sequencing analyses to determine which genes are expressed in the leaves when they are wet.

They discovered that in response to rain, several major immune-related genes are expressed and that these genes are regulated by immunosuppressive genes known as CAMTAs (calmodulin-binding transcription activators).

Because CAMTAs are regulated by calcium ions (Ca2+), the researchers hypothesized that rain increases Ca2+ concentrations in cells. By introducing GCaMP3 -a gene that fluoresces green when bound to Ca2+ -into the leaves, they were able to investigate how Ca2+ levels in Arabidopsis leaves change in response to rain. They discovered that when the leaves were exposed to rain, Ca2+ levels increased around trichomes on the leaf surfaces.

The findings suggested that trichomes detect rain as a risk factor and induce calcium waves (the transmission of localized increases in Ca2+ to surrounding areas) across the leaf, inactivating the immunosuppressor CAMTA and activating immune-related genes. To confirm this, they repeated the experiments with Arabidopsis mutants lacking trichomes, and the results showed that the propagation of calcium waves was compromised in the mutants.

"We confirmed that trichomes play a role in sensing rain as a risk factor and activating immune responses based on these findings," says Professor Tada. "Our findings suggest that we may be able to artificially improve plants' defenses against diseases at any time and for any length of time." We could use this technology to activate crops' immune responses when environmental conditions are harsh enough to cause disease in plants, resulting in stable crop yields."

(Source: Science Daily)