资源环境科技发展态势分析平台

Many corals harbour symbiotic dinoflagellate algae. The algae live inside coral cells in a specialized membrane compartment known as the symbiosome, which shares the photosynthetically fixed carbon with coral host cells while host cells provide inorganic carbon to the algae for photosynthesis(1). This endosymbiosis-which is critical for the maintenance of coral reef ecosystems-is increasingly threatened by environmental stressors that lead to coral bleaching (that is, the disruption of endosymbiosis), which in turn leads to coral death and the degradation of marine ecosystems(2). The molecular pathways that orchestrate the recognition, uptake and maintenance of algae in coral cells remain poorly understood. Here we report the chromosome-level genome assembly of aXeniaspecies of fast-growing soft coral(3), and use this species as a model to investigate coral-alga endosymbiosis. Single-cell RNA sequencing identified 16 cell clusters, including gastrodermal cells and cnidocytes, inXeniasp. We identified the endosymbiotic cell type, which expresses a distinct set of genes that are implicated in the recognition, phagocytosis and/or endocytosis, and maintenance of algae, as well as in the immune modulation of host coral cells. By couplingXeniasp. regeneration and single-cell RNA sequencing, we observed a dynamic lineage progression of the endosymbiotic cells. The conserved genes associated with endosymbiosis that are reported here may help to reveal common principles by which different corals take up or lose their endosymbionts.

The cryo-electron microscopy structure of a phycobilisome from the red alga Porphyridium purpureum reveals how aromatic interactions between the linker proteins and the chromophores drive a unidirectional transfer of energy.

Photosynthetic organisms have developed various light-harvesting systems to adapt to their environments(1). Phycobilisomes are large light-harvesting protein complexes found in cyanobacteria and red algae(2-4), although how the energies of the chromophores within these complexes are modulated by their environment is unclear. Here we report the cryo-electron microscopy structure of a 14.7-megadalton phycobilisome with a hemiellipsoidal shape from the red alga Porphyridium purpureum. Within this complex we determine the structures of 706 protein subunits, including 528 phycoerythrin, 72 phycocyanin, 46 allophycocyanin and 60 linker proteins. In addition, 1,598 chromophores are resolved comprising 1,430 phycoerythrobilin, 48 phycourobilin and 120 phycocyanobilin molecules. The markedly improved resolution of our structure compared with that of the phycobilisome of Griffithsia pacifica(5) enabled us to build an accurate atomic model of the P. purpureum phycobilisome system. The model reveals how the linker proteins affect the microenvironment of the chromophores, and suggests that interactions of the aromatic amino acids of the linker proteins with the chromophores may be a key factor in fine-tuning the energy states of the chromophores to ensure the efficient unidirectional transfer of energy.