Ph.D. Dissertation Defense - Guoxin Cui

Nov 18 2018 09:00 AM - Nov 18 2018 10:00 AM

Guoxin Cui

TITLE: Unravelling the Metabolic Interactions of the Aiptasia-Symbiodiniaceae Symbiosis
ADVISOR: Prof. Manuel Aranda
DATE: Sunday, November 18, 2018
TIME: 9:00 - 10:00 a.m.
LOCATION: Building 4 · Level 5 · Room 5209

ABSTRACT: Many omics-level studies have been undertaken on Aiptasia, however, our understanding of the genes and processes associated with symbiosis regulation and maintenance is still limited. To gain deeper insights into the molecular processes underlying this association,we investigated this relationship using multipronged approaches combining next generation sequencing with metabolomics and immunohistochemistry. 
We identified 731 high-confident symbiosis-associated genes using meta-analysis. Coupled with metabolomic profiling, we exposed that symbiont-derived carbon enables host recycling of ammonium into nonessential amino acids, which may serve as a regulatory mechanism to control symbiont growth through a carbon-dependent negative feedback of nitrogen availability to the symbiont. 
We then characterized two symbiosis-associated ammonium transporters (AMTs). Both of the proteins exhibit gastrodermis-specific localization in symbiotic anemones. Their tissue-specific localization consistent with the higher ammonium assimilation rate in gastrodermis of symbiotic Aiptasia as shown by 15N labeling and nanoscale secondary ion mass spectrometry (NanoSIMS). Inspired by the tissue-specific localization of AMTs, we investigated spatial expression of genes in Aiptasia. Our results suggested that symbiosis with Symbiodiniaceae is the main driver for transcriptional changes in Aiptasia. We focused on the phagosome-associated genes and identified several key factors involved in phagocytosis and the formation of symbiosome. Our study provided the first insights into the tissue specific complexity of gene expression in Aiptasia. 
To investigate symbiosis-induced response in symbiont and to find further evidence for the hypotheses generated from our host-focused analyses, we explored the growth and gene expression changes of Symbiodiniaceae in response to the limitations of three essential nutrients: nitrogen, phosphate, and iron, respectively. Comparisons of the expression patterns of in hospite Symbiodiniaceae to these nutrient limiting conditions showed a strong and significant correlation of gene expression profiles to the nitrogen-limited culture condition. This confirmed the nitrogen-limited growing condition of Symbiodiniaceae in hospite, and further supported our hypothesis that the host limits the availability of nitrogen, possibly to regulate symbiont cell density. 
In summary, we investigated different molecular aspects of symbiosis from both the host’s and symbiont’s perspective. This dissertation provides novel insights into the function of nitrogen, and the potential underlying molecular mechanisms, in the metabolic interactions between Aiptasia and Symbiodiniaceae

BIO: I am a molecular biologist focusing on the metabolic interactions in the cnidarian-dinoflagellate symbioses. Before coming to KAUST, I developed my expertise in a broad range of molecular, cellular, and biochemical techniques, and mainly focused on the research of plant science and structure biology. In my PhD studies, I developed and optimized several molecular tools to investigate the interactions between Aiptasia and Symbiodiniaceae in their symbiotic relationship. I aimed to integrated information from multiple omics levels to better understand the underlying molecular mechanisms, and validate the hypotheses raised from omics studies with different laboratory techniques at fine scales.