RecQ Helicases Function in Development, DNA Repair, and Gene Targeting in <i>Physcomitrella patens</i>

Abstract

RecQ DNA helicases are genome surveillance proteins found in all kingdoms of life. They are characterized best in humans, as mutations in <i>RecQ</i> genes lead to developmental abnormalities and diseases. To better understand RecQ functions in plants we concentrated on <i>Arabidopsis thaliana</i> and <i>Physcomitrella patens</i>, the model species predominantly used for studies on DNA repair and gene targeting. Phylogenetic analysis of the six <i>P. patens RecQ</i> genes revealed their orthologs in humans and plants. Because Arabidopsis and <i>P. patens</i> differ in their <i>RecQ4</i> and <i>RecQ6</i> genes, reporter and deletion moss mutants were generated and gene functions studied in reciprocal cross-species and cross-kingdom approaches. Both proteins can be found in meristematic moss tissues, although at low levels and with distinct expression patterns. <i>Pp</i>RecQ4 is involved in embryogenesis and in subsequent development as demonstrated by sterility of Δ<i>PpRecQ4</i> mutants and by morphological aberrations. Additionally, Δ<i>PpRecQ4</i> displays an increased sensitivity to DNA damages and an increased rate of gene targeting. Therefore, we conclude that <i>Pp</i>RecQ4 acts as a repressor of recombination. In contrast, <i>Pp</i>RecQ6 is not obviously important for moss development or DNA repair but does function as a potent enhancer of gene targeting.