Botryosphaerella sudeticus Transcriptome Profiling in Response to Nitrogen Starvation. Botryosphaerella sudetica strain:UTEX2629

Lipid storage is enhanced by nitrogen deprivation in numbers of green microalgal species. However, little is known about the metabolic pathways whose transcription levels are most significantly altered following nitrogen deprivation in green microalgae, especially the nonmodel species. To start gaining knowledge on this, we performed transcriptome profiling of the nonmodel green microalga Botryosphaerella sudeticus cells in response to nitrogen deprivation. Transcriptome of B. sudeticus is de novo assembled based on millions of HiSEQ short sequence reads using CLC Genomics Workbench software. The resulting non-redundant ESTs are annotated based on the best hits generated from the BLASTX sequence homology comparison against the “best” proteins in the model microalgae Chlamydomonas reinhardtii and Chlorella variabilis. By using a pathway-based approach according to KEGG databases, we show that ESTs encoding ribosomal proteins and photosynthetic functions are the most abundantly expressed ESTs in the rapidly growing B. sudeticus cells. On the other hand, ESTs encoding photosynthetic function but not the ribosomal proteins are most drastically down regulated upon nitrogen deprivation. This result implies that, upon nitrogen deprivation, phototropic growth of B. sudeticus cells is arrested by downregulation of energy intake but ribosomes function is preserved for synthesis of novel proteins required for gametogenesis and zygospore formation. Taken together, our analysis shows that similar transcriptional alterations of metabolic pathways occur in B. sudeticus and C. reinhardtii following nitrogen deprivation. We propose that the major pattern of the transcriptional response to nitrogen deprivation such as downregulation of photosynthesis is evolutionarily conserved in green microalgae for adaptation and survival.