The marine diatom Phaeodactylum tricornutum is a commercially viable species due to its bioactive substances and lipid productivity. Increasing attention has been paid to the isolation or genetic modification of species or strains with a rapid growth rate and large quantities of lipids. Furthermore, contamination of microzooplankton has been one of the major constraints in P. tricornutum large-scale cultivation, which adversely affects growth and greatly impedes the course of biomass production industrialization. Here, based on our previous transcriptomics of P. tricornutum, we found a novel gene (ID: 7202015, hereafter called Pt2015) which affects morphotype of P. tricornutum. Pt2015 protein is located in the plastid, which is highly homologous to part of the sequences of exosome component. The morphotype of the Pt2015 knockout strain (termed 2015KO) using CRISPR/Cas9 method is fusiform, but the Pt2015 overexpression strain (termed oeT) demonstrates a majority triradiate morphotype (a