Arabidopsis RTM2 gene is necessary for specific restriction of tobacco etch virus and encodes an unusual small heat shock-like protein

Arabidopsis plants have a system to specifically restrict the long-distance movement of tobacco etch potyvirus (TEV) without involving either hypersen sitive cell death or systemic acquired resistance. At least two dominant ge nes, RTM1 and RTM2, are necessary for this restriction. Through a series of coinfection experiments with heterologous viruses, the RTM1/RTM2-mediated restriction was shown to be highly specific for TEV. The RTM2 gene was isol ated by a map-based cloning strategy. Isolation of RTM2 was confirmed by tr ansgenic complementation and sequence analysis of wild-type and mutant alle les. The RTM2 gene product is a multidomain protein containing an N-termina l region with high similarity to plant small heat shock proteins (HSPs). Ph ylogenetic analysis revealed that the RTM2 small HSP-like domain is evoluti onarily distinct from each of the five known classes of plant small HSPs, U nlike most other plant genes encoding small HSPs, expression of the RTM2 ge ne was not induced by high temperature and did not contribute to thermotole rance of seedlings. The RTM2 gene product was also shown to contain a large C-terminal region with multiple repeating sequences.