A cyclic lipopeptide produced by an antagonistic bacterium relies on its tail and transient receptor potential‐type Ca²⁺ channels to immobilize a green alga

Abstract

Summary The antagonistic bacterium Pseudomonas protegens secretes the cyclic lipopeptide (CLiP) orfamide A, which triggers a Ca2+ 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 Ca2+ 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 Ca2+‐signal causing deflagellation. Molecular editing indicates that at least two distinct Ca2+‐signaling pathways are triggered. One is involved in deflagellation (Thr3 change, fatty acid tail shortened by 4C), whereas the other still causes an increase in cytosolic Ca2+ in the algal cells, but does not cause substantial deflagellation (Leu1 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 Ca2+ signaling, and that orfamide A uses a network of algal TRP‐type channels for deflagellation.

Exchange or Eliminate: The Secrets of Algal-Bacterial Relationships

“…In contrast to other cyclic lipopeptides, orfamide A does not seem to cause membrane pores [ 70 ]. The action of orfamide A depends on Ca 2+ channels of the transient receptor potential (TRP)-type, including TRP5, TRP11, TRP15 (also known as ADF-1), and TRP22 [ 104 ]. For its activity, the N-terminal amino acids of the linear part and the terminal fatty acid tail of orfamide A are highly important [ 104 ].…”

“…The action of orfamide A depends on Ca 2+ channels of the transient receptor potential (TRP)-type, including TRP5, TRP11, TRP15 (also known as ADF-1), and TRP22 [ 104 ]. For its activity, the N-terminal amino acids of the linear part and the terminal fatty acid tail of orfamide A are highly important [ 104 ]. One of the most potent toxins of P. protegens is the polyyne protegencin [ 101 ].…”

Compartment‐specific Ca2+ imaging in the green alga Chlamydomonas reinhardtii reveals high light‐induced chloroplast Ca2+ signatures

“…Some of these response mechanisms are conserved among unicellular microalgae, a large and diverse group of photosynthetic eukaryotes, where Ca 2+ is a crucial second messenger and a key player in signal transduction pathways (Edel et al ., 2017). In the green model alga Chlamydomonas reinhardtii , Ca 2+ signaling has been described in many motile responses, in stress responses to environmental stimuli, bacterial toxins and also in the regulation of photosynthesis (Wakabayashi et al ., 2009; Petroutsos et al ., 2011; Bickerton et al ., 2016; Rose et al ., 2021; Hou et al ., 2023). Many of these signal transduction pathways, however, still need to be characterized, and our knowledge on Ca 2+ signaling mechanisms in green algae remains limited.…”