SUMMARY The best‐known protein components of the plant cell wall have highly repetitive, proline‐rich sequences. The use of recombinant DNA approaches has enabled complete sequences of these proteins to be determined and features of the expression of the corresponding genes to be examined. These results, coupled with the use of immunological techniques, have shown that proline‐rich proteins are interesting probes to study developmental and defence processes in plants. In this review, the sequence and expression of different groups of proline‐rich proteins in plants are presented. These groups include hydroxyproline‐rich glycoproteins (HRGP) or extensins, proline‐rich proteins (PRP) and glycine‐rich proteins (GRP). The specific features of each group and the possible functions of these proteins are discussed, as well as the data available on the mechanisms controlling the expression of their corresponding genes.

An inhA promoter mutation could be considered as a marker for the determination of ETH resistance in India, where the use of LPA is being expanded.

The sequences of the genes coding for a hydroxyproline-rich glycoprotein from two varieties of maize (Zea mays, Ac1503 and W22), a teosinte (Zea diploperennis) and sorghum (Sorghum vulgare) have been obtained and compared. Distinct patterns of variability have been observed along their sequences. The 500 bp region immediately upstream of the TATA box is highly conserved in the Zea species and contains stretches of sequences also found in the sorghum gene. Further upstream, significant rearrangements are observed, even between the two maize varieties. These observations allow definition of a 5' region, which is common to the four genes and is probably essential for their expression. The 3' end shows variability, mostly due to small duplications and single nucleotide substitutions. There is an intron present in this region showing a high degree of sequence conservation among the four genes analyzed. The coding region is the most divergent, but variability arises from duplications of fragments coding for similar protein blocks and from single nucleotide substitutions. These results indicate that a number of distinct mechanisms (probably point mutation, transposon insertion and excision, homologous recombination and unequal crossing-over) are active in the production of sequence variability in maize and related species. They are revealed in different parts of the gene, probably as the result of the different types of functional constraints acting on them, and of the specific nature of the sequence in each region.

Variable-size fragments of the four yeast acidic ribosomal protein genes rpYP1 alpha, rpYP1 beta, rpYP2 alpha and rpYP2 beta were fused to the LacZ gene in the vector series YEp356-358. The constructs were used to transform wild-type Saccharomyces cerevisiae and several gene-disrupted strains lacking different acidic ribosomal protein genes. The distribution of the chimeric proteins between the cytoplasm and the ribosomes, tested as beta-galactosidase activity, was estimated. Hybrid proteins containing around a minimum of 65-75 amino acids from their amino-terminal domain are able to bind to the ribosomes in the presence of the complete native proteins. Hybrid proteins containing no more than 36 amino terminal amino acids bind to the ribosomes in the absence of a competing native protein. The fused YP1-beta-galactosidase proteins are also able to form a complex with the native YP2 type proteins, promoting their binding to the ribosome. The stability of the hybrid polypeptides seems to be inversely proportional to the size of their P protein fragment. These results indicate that only the amino-terminal domain of the eukaryotic P proteins is needed for the P1-P2 complex formation required for interaction with the ribosome. The highly conserved P protein carboxyl end is not implicated in the binding to the particles and is exposed to the medium.