In vivo transfer of barley stripe mosaic hordeivirus ribonucleotides to the 5' terminus of maize stripe tenuivirus RNAs.

The Tenuivirus maize stripe virus (MStV) shares many properties with viruses in the genus Phlebovirus of the family Bunyaviridae. Besides genome organization and gene expression strategies, one property shared by these plant- and vertebrate-infecting viruses is that transcription gives rise to virus-specific mRNAs containing nonviral 5'-terminal nucleotide sequences. The 5'-terminal nucleotides are believed to be derived from host mRNA sequences as a result of "cap-snatching." We investigated whether specific nucleotide sequences could serve as primer donors for cap-snatching in vivo. Barley (Hordeum vulgare) plants were singly and doubly infected with MStV and the Hordeivirus barley stripe mosaic virus (BSMV). A reverse transcription-PCR assay was used to identify chimeric BSMV/MStV RNAs. Specific reverse transcription-PCR products were detected from doubly infected plants by using one PCR primer corresponding to the 5' termini of the BSMV RNAs (alpha, beta, and gamma) and a second primer complementary to MStV RNA 4. The resulting cDNAs were cloned, and nucleotide sequence analysis showed them to be chimeric, containing BSMV 5'-terminal sequences as well as MStV RNA 4 sequences. All clones contained the BSMV RNA 5' primer nucleotide sequence, but they also showed characteristics common to Tenuivirus mRNAs. More than 80% of the clones contained BSMV RNA nucleotides not present on the PCR primer. Several lacked the exact 5' terminus of MStV RNA 4, a feature also seen for viruses in the Bunyaviridae. These data show that heterologous virus RNAs (BSMV) can serve as primer donors for MStV mRNA capped RNA-primed transcription in doubly infected plants.

Maize stripe tenuivirus RNA2 transcripts in plant and insect hosts and analysis of pvc2, a protein similar to the Phlebovirus virion membrane glycoproteins.

The complete sequence of the maize stripe tenuivirus (MStV) RNA2 was determined (3337 nucleotides). RNA2 contains two large open reading frames (ORFs) arranged in an ambisense orientation and specific RNAs of ca. 700 and 2600 nucleotides corresponding to the ORFs were detected in MStV-infected plants and planthoppers. The deduced amino acid sequence of the 23,500 MW protein (pv2) encoded by viral RNA2 (vRNA2) was similar to proteins encoded by the rice stripe (RStV) and rice hoja blanca tenuiviruses vRNA2. Sequence analysis suggested that pv2 is membrane associated. The 93,900 MW protein (pvc2) encoded by viral complementary MStV RNA2 (vcRNA2) was similar to the 94,000 MW protein of RStV RNA2 and to the virion membrane glycoproteins for Phlebovirus members of the Bunyaviridae. The phlebovirus glycoprotein cleavage site was similar to a region in the MStV and RStV proteins suggesting that the tenuivirus pvc2 may be processed analogous to the phlebovirus glycoproteins.

Differential expression of phenylalanine ammonia-lyase and chalcone synthase during soybean nodule development.

We have used conserved and nonconserved regions of cDNA clones for phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) isolated from a soybean-nodule cDNA library to monitor the expression of members of the two gene families during the early stages of the soybean-Bradyrhizobium japonicum symbiosis. Our results demonstrate that subsets of the PAL and CHS gene families are specifically induced in soybean roots after infection with B. japonicum. Furthermore, by analyzing a supernodulating mutant line of soybean that differs from the wild-type parent in the number of successful infections, we show that the induction of PAL and CHS is related to postinfection events. Nodulated roots formed by a Nod+ Fix- strain of B. japonicum, resembling a pathogenic association, display induction of another distinct set of PAL and CHS genes. Our results suggest that the symbiosis-specific PAL and CHS genes in soybean are not induced by stress or pathogen interaction.