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Title: MOVEMENT OF POTATO SPINDLE TUBER VIROID REVEALS REGULATORY POINTS OF PHLOEM-MEDIATED RNA TRAFFIC

Author
item ZHU, Y - OHIO STATE UNIV
item QI, Y - OHIO STATE UNIV
item XUN, Y - OHIO STATE UNIV
item Owens, Robert
item DING, B - OHIO STATE UNIV

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Viroids are the smallest pathogenic agents yet described - small (246-399 nucleotides), circular RNA molecules that lack both the messenger RNA activity and protein coat characteristic of conventional viruses. Thus far, viroids are only known to infect plants where they cause a number of economically significant diseases. In this study, potato spindle tuber viroid (PSTVd) was used as a "probe" to characterize the process by which RNA molecules enter and exit the vascular system of the host plant. We are studying RNA transport in the phloem because the ability of viroids to move long distances is a critical step in establishing a generalized infection. There are no known sources of conventional genetic resistance to viroid disease, and any strategy that inhibits long distance viroid movement should render the host plant resistant/immune to viroid infection. This article will be of greatest interest to research scientists and others working in the general area of plant molecular biology

Technical Abstract: Increasing evidence indicates that the phloem mediates traffic of selected RNAs within a plant. How an RNA enters, moves in, and exits the phloem is poorly understood. Potato spindle tuber viroid (PSTVd) is a pathogenic RNA that does not encode proteins and is not encapsidated, and yet it replicates autonomously and traffics systemically within an infected plant. The viroid RNA genome must interact directly with cellular factors to accomplish these functions and is, therefore, an excellent probe to study mechanisms that regulate RNA traffic. Our analyses of PSTVd traffic in Nicotiana benthamiana yielded evidence that PSTVd movement within sieve tubes does not simply follow mass flow from source to sink organs. Rather, this RNA is transported into selective sink organs. Furthermore, two PSTVd mutants can enter the phloem to spread systemically but cannot exit the phloem in systemic leaves of tobacco. A viroid most likely has evolved structural motifs that mimic endogenous plant RNA motifs so that they are recognized by cellular factors for traffic. Thus, analyses of PSTVd traffic functions may provide insights about endogenous mechanisms that control phloem entry, transport, and exit of RNAs.