A cyclic lipopeptide produced by an antagonistic bacterium relies on its tail and transient receptor potential‐type Ca<sup>2+</sup> channels to immobilize a green alga
Yu Hou, Yuko Bando, David Carrasco Flores, Vivien Hotter, Ritam Das, Bastian Schiweck, Tommy Melzer, Hans‐Dieter Arndt, Maria Mittag
Abstract
Summary The antagonistic bacterium Pseudomonas protegens secretes the cyclic lipopeptide (CLiP) orfamide A, which triggers a Ca 2+ signal causing rapid deflagellation of the microalga Chlamydomonas reinhardtii . We performed chemical synthesis of orfamide A derivatives and used an aequorin reporter line to measure their Ca 2+ responses. Immobilization of algae was studied using a modulator and mutants of transient receptor potential (TRP)‐type channels. By investigating targeted synthetic orfamide A derivatives, we found that N ‐terminal amino acids of the linear part and the terminal fatty acid region are important for the specificity of the Ca 2+ ‐signal causing deflagellation. Molecular editing indicates that at least two distinct Ca 2+ ‐signaling pathways are triggered. One is involved in deflagellation (Thr 3 change, fatty acid tail shortened by 4C), whereas the other still causes an increase in cytosolic Ca 2+ in the algal cells, but does not cause substantial deflagellation (Leu 1 change, fatty acid hydroxylation, fatty acid changes by 2C). Using mutants, we define four TRP‐type channels that are involved in orfamide A signaling; only one (ADF1) responds additionally to low pH. These results suggest that the linear part of the CLiP plays one major role in Ca 2+ signaling, and that orfamide A uses a network of algal TRP‐type channels for deflagellation.