Important role of plastid ion channels in plant stress response identified

When plants are attacked by herbivores or pathogens, they must respond rapidly while also preparing for potential future attacks. Calcium, a cellular second messenger, and the plant hormone jasmonic acid play important roles in this response. Within seconds of an injury, the plant generates calcium waves that relay information about the attack. At the same time, the synthesis of jasmonic acid is initiated in the chloroplast, triggering, through several intermediate steps, the expression of defense genes in the cell nucleus.

Until now, however, exactly how rapid calcium signals reach chloroplasts and how they are linked to jasmonic-acid-mediated defense was largely unknown. LMU researchers led by professors Hans-Henning Kunz and Christian Grimm have now shown that specific cation channels known as PECs play an important role in connecting the two processes.

The channels mediate rapid cation fluxes into chloroplasts, which the team was able to record directly for the first time via electrophysiological measurements on isolated organelles from the model organism Arabidopsis thaliana. Intriguingly, jasmonic acid synthesis activated by herbivores or pathogens increases the production of PEC channels within a few hours, and PEC levels remain elevated for several days. The work is published in the Proceedings of the National Academy of Sciences.

“If the stress persists or recurs—for example, through a subsequent stress stimulus—this can then trigger a stronger calcium signal in the chloroplast,” says lead author Susanne Mühlbauer. This, in turn, promotes the synthesis of additional jasmonic acid and primes the plant to mount a faster and more sustained defense response.

As the researchers demonstrated, this can increase resistance to the fungus Botrytis cinerea. “PECs thus help plants use the experience of an initial stress to prepare for further attacks and strengthen their long-term defenses,” Kunz says.

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