ANNEXIN1 mediates calcium-dependent systemic defense in Arabidopsis plants upon herbivory and wounding.

Cellular calcium transients are endogenous signals involved in local and systemic signaling and defense activation upon environmental stress, including wounding and herbivory. Still, not all Ca2+ channels contributing to the signaling have been identified, nor are their modes of action fully known. Plant annexins are proteins capable of binding to anionic phospholipids and can exhibit calcium channel-like activity. Arabidopsis ANNEXIN1 is suggested to contribute to calcium transport. Here, we report that wounding- and simulated herbivory-induced cytosolic free calcium elevation was impaired in systemic leaves in ann1 loss of function plants. We provide evidence for a role of ANNEXIN1 in local and systemic defense of plants attacked by herbivorous Spodoptera littoralis larvae. Bioassays identified ANNEXIN1 as a positive defense regulator. S. littoralis feeding on ann1 gained significantly more weight compared with larvae feeding on wild-type, while those feeding on ANNEXIN1 overexpressing lines gained less weight. Herbivory and wounding both induced defense-related responses on treated leaves such as jasmonate accumulation and defense gene expression. These responses remained local and were strongly reduced in systemic leaves in ann1 plants. Our results indicate that ANNEXIN1 plays an important role in activation of systemic rather than local defense in plants attacked by herbivorous insects.