One of my students wanted to figure out how to make animals photosynthesize. Well, this article indicates that sea slugs have figured out how eat and digest the algae but keep the algal chloroplasts alive in their guts so the sea slug can use the fats and carbohydrates the chloroplasts produce (the stealing of the algal organelles is called kleptoplasty). To maintain the chloroplasts, the slugs have actually had to incorporate some of the algae DNA into their own chromosomes–this is called horizontal gene transfer and it’s what scientists try to do with gene therapies.
More details here.
