No abstract

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 6. japonicum. Furthermore, by analyzing a supernodulating mutant line of soybean that differs from the wildtype 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 6. japonicum, resembling a pathogenic association, display induction of another distinct set of PAL and CHS genes. Our results suggest that the symbiosisspecific PAL and CHS genes in soybean are not induced by stress or pathogen interaction.

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 capsnatching 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 BSMV͞MStV 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 (␣, ␤, and ␥) 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.