Arsenic (As) is a ubiquitous element that is widespread in the environment and causes numerous health problems.Biomethylation of As has implications for its mobility and toxicity. Photosynthetic organisms may play a significant role in As geochemical cycling by methylating it to different As species, but little is known about the mechanisms of methylation. Methylated As species have been found in many photosynthetic organisms, and several arsenite S-adenosylmethionine (SAM) methyltransferases have been characterized in cyanobacteria and algae. However,higher plants may not have the ability to methylate As.Instead, methylated arsenicals in plants probably originate from microorganisms in soils and the rhizosphere.Here, we propose possible approaches for developing ‘smart’ photosynthetic organisms with an enhanced and sensitive biomethylation capacity for bioremediation and safer food.