Paulinella chromatophora is one of the few cercozoans that is autotrophic, carrying out aerobic photosynthesis with its two elongated "cyanelles." The cyanelles are contained within vesicles of the host cell, and each is derived from a cyanobacterium, though not the same type of cyanobacterium that gave rise to the chloroplasts of algae and plants.

A crucial photosynthetic gene of the cyanobacterium that gave rise to the cyanelle is called psaE. This gene is present in the nuclear genome of the cercozoan, but is not in the genome of the cyanelle. This is evidence of
A)transduction by a phage that infects both prokaryotes and eukaryotes.
B)genetic recombination involving a protist and an archaean.
C)the origin of photosynthesis in protists.
D)reciprocal mutations in the cyanelle and nuclear genomes.
E)horizontal gene transfer from bacterium to eukaryotes.