Significance Translation is the process by which ribosomes decode information in RNA to produce proteins. The resulting proteins constitute cellular structures and regulate diverse functions in all organisms. Translation also affects mRNA stability. As the final step of the central dogma, translation can alter protein production more rapidly than transcription in a changing environment. However, a robust experimental method to define the landscape of the translatome has not been established in many organisms. We developed an advanced experimental approach and used it to discover proteins missed in the annotation of the Arabidopsis genome. This study confirmed computationally predicted noncanonical translation events and uncovered unannotated small proteins that likely have important functions in plants.