A conserved transcription factor mediates nuclear control of organelle biogenesis in anciently diverged land plants.

Land plant chloroplasts evolved from those found in the green algae. During land plant evolution, nuclear regulatory mechanisms have been modified to produce morphologically and functionally diverse chloroplasts in distinct developmental contexts. At least some of these mechanisms evolved independently in different plant lineages. In angiosperms, GOLDEN2-LIKE (GLK) transcription factors regulate the development of at least three chloroplast types. To determine whether GLK-mediated regulation of chloroplast development evolved within angiosperms or is a plesiomorphy within land plants, gene function was examined in the moss Physcomitrella patens. Gene expression patterns and loss-of-function mutant phenotypes suggested that GLK gene function is conserved between P. patens and Arabidopsis thaliana, species that diverged >400 million years ago. In support of this suggestion, moss genes partially complement Arabidopsis loss-of-function mutants. Therefore, GLK-mediated regulation of chloroplast development defines one of the most ancient conserved regulatory mechanisms identified in the plant kingdom.