Cauliflower mosaic virus infection stimulates lipid transfer protein gene expression in Arabidopsis

Lipid transfer proteins (LTPs), are encoded in plants by multi-gene families, and have been implicated in the defence response to bacterial and fungal infection. Levels of LTP transcripts in Arabidopsis systemically infected with either a mild or a severe isolate of CaMV, were elevated approximately 3-5-fold compared to uninfected controls. In CaMV-infected transgenic Arabidopsis containing a GUS reporter gene under the control of an LTP promoter from Brassica napus, high levels of GUS in the leaves, root hairs and lateral root were observed, whereas mock inoculated controls showed markedly lower expression. A second construct, with one of the Arabidopsis LTP promoters, did not show increased GUS expression following infection. CaMV gene VI is a major determinant of symptom phenotype and constitutive transgene-mediated expression induces a symptom-like phenotype, Levels of LTP mRNA were elevated in transgenic plants expressing high levels of gene VI protein, and double transgenics that contained the BnLTP::GUS transgene and expressed high levels of gene VI protein, stained intensely for GUS activity. These observations suggest that the response to systemic infection by CaMV includes transcription of some, but probably not all of the LTP genes. Expression of CaMV gene VI appears to be important in triggering this process.