A Land Plant-specific Transcription Factor Directly Enhances DNA-dependent RNA Polymerase II Transcribing A Pathogenic Noncoding RNA Template
Y. WANG (1), J. Qu (2), S. Ji (3), A. Wallace (2), J. Wu (2), Y. Li (3), V. Gopalan (2), B. Ding (2) (1) The Ohio State University, U.S.A.; (2) The Ohio State University, U.S.A.; (3) Peking University, China

Some DNA-dependent RNA polymerases (DdRP) possess RNA-dependent RNA polymerase activity, as was first discovered in the replication of Potato spindle tuber viroid (PSTVd) in tomato. Recent studies revealed this activity in bacteria and mammals as pivotal regulatory mechanisms for gene expression. Here, we used PSTVd as a model to uncover factors essential for RNA-templated transcription by DdRP. PSTVd replication in the nucleoplasm generates (-)-PSTVd intermediates and (+)-PSTVd copies. We found that canonical 9-zinc finger (ZF) Transcription Factor IIIA (TFIIIA-9ZF) as well as its variant 7-ZF TFIIIA (TFIIIA-7ZF) interacted with (+)-PSTVd, but TFIIIA-7ZF interacted with (-)-PSTVd. Suppression of TFIIIA-7ZF reduced PSTVd replication, while overexpression of TFIIIA-7ZF enhanced PSTVd replication in planta. Consistent with the locale of PSTVd replication, TFIIIA-7ZF was found in the nucleoplasm and nucleolus, in contrast to the strictly nucleolar locale of TFIIIA-9ZF. Footprinting assays revealed that TFIIIA-7ZF bound to a region of PSTVd critical for initiating transcription. Furthermore, TFIIIA-7ZF strongly enhanced the in vitro transcription of circular (+)-PSTVd by partially purified Pol II. Together, our results identify TFIIIA-7ZF as a dedicated cellular transcription factor in a DdRP-catalyzed RNA-templated transcription, highlighting both the extraordinary evolutionary adaptation of viroids and the potential of DdRPs for a broader role in cellular processes. 

Abstract Number: C5-4, P10-343
Session Type: Concurrent