The photorespiratory pathway is involved in the defense response to powdery mildew infection in chestnut rose.

Chestnut rose (Rosa roxburghii Tratt), a non-domesticated potential fruit crop, is susceptible to infection by powdery mildew. A small-scale customized macro-array was assembled with cDNA clones from a suppression subtractive hybridization library enriched for defense transcripts and used to screen for differentially expressed genes induced by powdery mildew infection. Three photorespiratory genes, encoding the small subunit of RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase), RuBisCO activase and serine-glyoxylate aminotransferase, were identified in this screen. Quantitative RT-PCR analysis of these three genes showed that they were significantly up-regulated 16 h after the host was inoculated with powdery mildew, and assays at the enzyme level confirmed high levels of enzymatic activity 24 h after infection. Of six phytohormones tested, salicylic acid (SA) noticeably induced their expression, and HPLC analysis showed that SA accumulated in the leaves after fungal infection.