A SMALL RNA RESEMBLING THE BEET WESTERN YELLOWS LUTEOVIRUS ST9-ASSOCIATED RNA IS A COMPONENT OF THE CALIFORNIA CARROT MOTLEY DWARF COMPLEX

Virions were purified from Anthriscus cerefolium or Coriandrum sativum plants infected with the viruses that cause California carrot motley dwarf. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of vi rion preparations yielded a single prominent protein species of approx imately 28,000 molecular weight; however, denaturing agarose gel elect rophoresis showed that virions contained three prominent single-strand ed RNAs of approximately 5.6, 4.2, and 2.8 kb. Northern hybridization analyses, using transcripts generated from cloned cDNAs that correspon ded to each of the virion RNAs, showed that the 5.6- and 4.2-kb RNAs w ere the genomic RNAs of the carrot red leaf luteovirus (CRLV) and the carrot mottle umbravirus (CMoV), respectively. Virions also contained an approximately 1.3-kb RNA related to the CMoV genomic RNA. The 2.8-k b RNA did not hybridize with CRLV or CMoV cRNA probes. Analysis of nat urally infected carrot (Daucus carota) plants showed that CRLV, CMoV, and the 2.8-kb RNA were always present in carrot motley dwarf-affected plants. Greenhouse aphid-and mechanical-transmission experiments show ed that the 2.8-kb RNA was consistently present in plants also infecte d by both CRLV and CMoV, but never in plants infected by only CMoV. Ne ar full-length cloned cDNAs corresponding to the 2.8-kb RNA were prepa red, and the complete nucleotide sequence was determined to be 2,835 n ucleotides. Two large open reading frames (ORFs), 1a and Ib, were pres ent within the sequence and were separated by an amber (UAG) stop codo n. A third ORF (ORF 2), capable of encoding a protein of 4,289 molecul ar weight, was located near the 3' terminus. BLASTP results showed tha t the 2.8-kb RNA was most closely related to the beet western yellows luteovirus (BWYV) ST9-associated RNA. Based on its biological and mole cular characteristics, we have named the 2.8-kb RNA the CRLV-associate d RNA (CRLVaRNA).