A novel type of kleptoplastidy in Dinophysis (Dinophyceae): presence of haptophyte-type plastid in Dinophysis mitra

Red-fluorescent, non-phycobilin-containing plastids were found in the heterotrophic dinoflagellate, Dinophysis mitra. Transmission electron microscopy showed that they contained a three-layer thylakoid, the absence of girdle lamella, and an embedded pyrenoid with thylakoid intrusions. These characteristics all coincide with haptophyte plastids. Phylogenetic analysis of the plastid small-subunit ribosomal DNA (SSU rDNA) revealed that the Dinophysis mitra sequences are distantly related to those of phycobilin-containing Dinophysis species and are positioned within a lineage of haptophytes belonging to Prymnesiophyceae. Because the plastid SSU rDNA sequences of Dinophysis mitra showed significant heterogeneity, despite being derived from a single species, it is highly likely that they were not established as plastids through an evolutionary process but are "kleptoplastids" (temporally stolen plastids) from multiple sources of haptophytes in the environment. We deduced that Dinophysis mitra takes up haptophytes myzocytotically and selectively retains the plastid with surrounding plastidal membranes, whereas other haptophyte cell components are degraded. This represents another type of kleptoplastidy in the Dinophysis species, which mostly harbor cryptophyte plastids, and is the first evidence of kleptoplastidy originating from haptophytes.