Transcriptome analysis of Chlamydomonas reinhardtii cultivated in liquid cultures and in S3-D
Photosynthetic protists, named microalgae, are key players in global primary production. The green microalga Chlamydomonas reinhardtii is a well-studied model organism. In nature, it dwells in wet and highly inhomogeneous soil, which is not mimicked by standard liquid laboratory conditions. Here, we maintained the algae in a liquid environment with spatially structured 3-D components (S3-D) recreating natural conditions. We perform whole transcriptome sequencing, immunoblotting, fluorescence microscopy, and Raman microspectroscopy to characterize the algae in S3-D versus homogeneous conditions. The algal cells undergo a metamorphosis-like process when transitioned from homogeneous aquatic to a terrestrial-like lifestyle. S3-D results in a reduced cell size, creates many cells with double-layered cell wall s, reduces the length of the cilia, and enlarges the eyespot. Whole transcriptome sequencing reveals alterations in >5,000 transcripts. Four key photoreceptors including CRY -DASH1 and phototropin governing the metabolism of the chloroplast along with its eyespot are altered in their protein expression. Consequently, photosynthetic pigments and starch levels vary as well as starch distribution patterns. Fitness against antagonistic bacteria is enhanced while involved Ca2+ channel transcripts are downregulated. This study highlights the profound impact of S3-D initiating processes inaccessible under homogeneous laboratory conditions. Thus, overexpression lines for carotenoids and starch are naturally created.