UC Merced

The reef-building coral species of tropical seas worldwide, together with their algal endosymbionts, drive the productivity of coral reef ecosystems by forming the three-dimensional structure of reefs and by functioning as primary producers. The photosynthetic endosymbionts (of the genus Symbiodinium) are key to the role of primary production. This mutualism is under intense investigation because high temperature anomalies in coastal seas trigger a breakdown in the symbiosis known as coral bleaching. As sea surface temperatures rise due to global climate change, understanding the physiological, cellular, and molecular mechanisms underlying coral bleaching is imperative to predict whether corals will survive this age of human-induced environmental degradation. Operating under this impetus, genomic approaches to studying the coral-algal symbiosis and its breakdown, such as cDNA microarrays, offer great promise. Microarrays allow for the rapid quantification of gene expression for thousands of genes in a single snapshot. In focusing on thermal stress and bleaching microarray experiments in the Caribbean corals Acropora palmata and Montastraea faveolata, I have found that the following cellular processes/components are affected during bleaching: oxidative stress, chaperone activity, the glyoxylate cycle, DNA repair, calcium homeostasis, cell death, the extracellular matrix, cell cycle progression, the actin cytoskeleton, nitric oxide signaling, and metabolite transfer between host and symbiont. Specific differentially expressed genes represent subjects of further investigation that are likely involved in coral-specific processes such as calcification, symbiosis maintenance, and bleaching. Furthermore, my experiments have revealed the striking effects that both stress and different symbiont genotypes can have on the host transcriptome. It is hypothesized that the host transcriptome is shaped by the competing effects of stress and the symbionts, and that this balance depends on both technical parameters (e.g. acclimation time, thermal treatment) and biological factors (e.g. species-specific stress sensitivities).