Use the Following Information to Answer the Question

Use the following information to answer the question.
Paulinella chromatophora is one of the few cercozoans that is autotrophic, carrying out aerobic photosynthesis with its two elongated "chromatophores." The chromatophores 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 chromatophore is called psaE. This gene is present in the nuclear genome of the cercozoan, but is not in the genome of the chromatophore. This is evidence of ________.

A) reciprocal mutations in the chromatophore and nuclear genomes
B) horizontal gene transfer from bacterium to eukaryotes
C) genetic recombination involving a protist and an archaean
D) transduction by a phage that infects both prokaryotes and eukaryotes