We are pleased to announce that the latest release of the Plant Ontology, version #21, is now available on our browser at http://www.plantontology.org One major change you may see is that on August 1, 2015, all the ontology files and issue tracker were moved to a shiny new GitHub Site: (https://github.com/Planteome/plant-ontology) as part of the Planteome Project. Please update your local browser bookmarks, and come check out the new functionalities. * This full release of the PO features the addition of 37 new PO terms, for both the ''Plant Anatomical Entity (PAE)'' (31) and ''Plant Structure Development Stage (PSDS)'' (6) branches of the ontology. * Names have been revised for 23 PAE terms and 21 PSDS terms, and definitions of many more terms have also been revised and updated. * This Release also includes new and updated annotation data for five species: Maize (307), Arabidopsis (3339), soybean (34), Medicago (81), and tomato (147), generated as part of the Plant Phenotype Pilot Project (http://www.phenotypercn.org/?p=1099 ) and compiled by the POC. The rice annotations (279) were added in Version #20. All these annotations refer to genes associated with characterized mutant phenotypes. * Additional annotation data was contributed by our collaborators for Soybean QTLs (SoyBase) and and Arabidopsis thaliana genes (TAIR). For complete information about the changes in Release #21, please see: http://wiki.plantontology.org/index.php/Release_21 and refer to the Release Notes on PO home page: (http://plantontology.org/docs/release_notes/index.html).