‘Independent and parallel evolution of new genes by gene duplication in two origins of C4 photosynthesis provides new insight into the mechanism of phloem loading in C4 species.’
http://mbe.oxfordjournals.org/content/early/2016/03/24/molbev.msw057.abstract?sid=8cecb98a-5ee1-4757-8974-ee8447e7b593
c4rice.com 