To extend the terms associated with C. reinhartdii genes, functional terms were inferred by homology to the annotation set of the plant Arabidop — sis thaliana (thale cress). Identification of orthologous proteins was based on sequence similarity and subsequent filtering of the results by retain­ing only mutual best hits between the two sets of protein sequences. The corresponding Arabidopsis thaliana annotation was used to supplement GO terms and was similarly expanded to contain term ancestry. The A. thaliana annotations of the MapMan Ontology [33] and MetaCyc Pathway database [2] were also used to provide more complete annotation coverage of the C. reinhardii genome.