Small shifts, big ripples: multi-omics studies reveal how ambient temperatures govern Chlamydomonas cellular responses

Photosynthetic protists known as microalgae face increasing temperatures due to global climate change. The green biflagellate alga Chlamydomonas reinhardtii is commonly found in moist soil and serves as a model for investigating these effects. While responses to extreme thermal stress are well characterized, much less is known about the impact of modest, non-extreme temperature shifts. Understanding microalgal responses to subtle temperature changes is critical, as these primary producers drive ecosystem productivity and food web dynamics. Even small shifts may alter algal fitness and reshape interactions with other microbes. Here, C. reinhardtii grew at non-stress, ambient temperatures ranging from 18 {degrees}C to 33 {degrees}C. Transcriptomic profiling revealed extensive reorganization, with over 5,000 transcripts significantly affected, including those involved in algal-bacterial interactions, photoreception, RNA and lipid metabolism, cilia formation, and the secretome. Proteomic analysis of isolated cilia and secreted proteins corroborated these findings, uncovering major changes in abundance within these sub-proteomes, particularly intraflagellar transport (IFT) complexes in cilia and mating-related proteins in the secretome that are both upregulated at higher temperature. Together, these molecular alterations resulted in pronounced changes in growth, cell size, cilia length, swimming behavior, mating ability and bacterial antagonism. These data emphasize major cellular responses upon small temperature shifts.