Bean Ribonuclease‐Like Pathogenesis‐Related Protein Genes (Ypr10) Display Complex Patterns of Developmental, Dark‐Induced and Exogenous‐Stimulus‐Dependent Expression

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Abstract
The intracellular pathogenesis‐related (PR) proteins of common bean (Phaseolus vulgaris L.) are encoded by a highly polymorphic family of at least 20 genes. One member, the Ypr10*c gene, has been isolated and characterised. The deduced amino acid sequence of the encoded protein, PR‐10, exhibits similarities to tree‐pollen allergens, to food allergens from celery and apple and to ginseng ribonuclease peptide sequences. We show by RNA blot analysis that the Ypr10 gene family, including Ypr10*c, is strongly expressed in bean roots. In leaves Ypr10 transcript levels are low in young and mature stages but are elevated during senescence and in diseased states. Dark treatment of leaves causes strong induction of Ypr10 transcripts, which is reversible by light, and diurnal rhythms of transcript accumulation during the night are observed. Ypr10 genes are responsive to external stimuli related to pathogen‐defence such as glutathione or salicylic acid. Transcriptional activity of a Ypr10*c promoter–β‐glucuronidase fusion gene in transgenic tobacco was observed in roots, in developing xylem and phloem of stems, and in the blade of senescent leaves, with highest levels at the onset of senescence. The most striking characteristic of developmental expression was the specific localisation of β‐glucuronidase activity in the transmitting tract of styles in flowers at anthesis. Feeding of various pathogen‐related and stress‐related stimuli to young tobacco leaves led to accumulation of GUS activity in leaf blades. We identify considerable spatio‐temporal similarities between reported expression patterns of Ypr10 genes and ribonuclease genes, which, together with the significant sequence similarity to the ginseng ribonuclease, support the hypothesis of a ribonuclease function for PR‐10 proteins and allow the prediction of possible biological roles.