| Summary: | PARP proteins are highly conserved homologs among the eukaryotic poly (ADP-ribose) polymerases. After activation, ADP-ribose polymers are synthesized on a series of ribozymes that use NAD+ as a substrate. PARPs participate in the regulation of various important biological processes, such as plant growth, development, and stress response. In this study, we characterized the homologue of <i>PARP1</i> in <i>B. rapa</i> using RNA interference (RNAi) to reveal the underlying mechanism responding to drought stress. Bioinformatics and expression pattern analyses demonstrated that two copy numbers of <i>PARP1</i> genes (Br<i>PARP1.A03</i> and Br<i>PARP1.A05</i>) in <i>B. rapa</i> following a whole-genome triplication (WGT) event were retained compared with <i>Arabidopsis</i>, but only Br<i>PARP1.A03</i> was predominantly transcribed in plant roots. Silencing of Br<i>PARP1</i> could markedly promote root growth and development, probably via regulating cell division, and the transgenic <i>Brassica</i> lines showed more tolerance under drought treatment, accompanied with substantial alterations including accumulated proline contents, significantly reduced malondialdehyde, and increased antioxidative enzyme activity. In addition, the findings showed that the expression of stress-responsive genes, as well as reactive oxygen species (ROS)-scavenging related genes, was largely reinforced in the transgenic lines under drought stress. In general, these results indicated that Br<i>PARP1</i> likely responds to drought stress by regulating root growth and the expression of stress-related genes to cope with adverse conditions in <i>B. rapa.</i>
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