Calcium Signalling in Plant Biotic Interactions

Calcium (Ca(2+)) is a universal second messenger involved in various cellular processes, leading to plant development and to biotic and abiotic stress responses. Intracellular variation in free Ca(2+) concentration is among the earliest events following the plant perception of environmental change. These Ca(2+) variations differ in their spatio-temporal properties according to the nature, strength and duration of the stimulus. However, their conversion into biological responses requires Ca(2+) sensors for decoding and relaying. The occurrence in plants of calmodulin (CaM) but also of other sets of plant-specific Ca(2+) sensors such as calmodulin-like proteins (CMLs), Ca(2+)-dependent protein kinases (CDPKs) and calcineurin B-like proteins (CBLs) indicate that plants possess specific tools and machineries to convert Ca(2+) signals into appropriate responses. Here, we focus on recent progress made in monitoring the generation of Ca(2+) signals at the whole plant or cell level and their long distance propagation during biotic interactions. The contribution of CaM/CMLs and CDPKs in plant immune responses mounted against bacteria, fungi, viruses and insects are also presented.