Ozone and nitric oxide induce cGMP-dependent and -independent transcription of defence genes in tobacco

Here, we analyse the temporal signatures of ozone (O-3)-induced hydrogen peroxide (H2O2) and nitric oxide (NO) and the role of the second messenger guanosine 3',5'-cyclic monophosphate (cGMP) in transcriptional changes of genes diagnostic for biotic and abiotic stress responses. Within 90 min O-3 induced H2O2 and NO peaks and we demonstrate that NO donors cause rapid H2O2 accumulation in tobacco (Nicotiana tabacum) leaf. Ozone also causes highly significant, late (> 2 h) and sustained cGMP increases, suggesting that the second messenger may not be required in all early (< 2 h) responses to O-3, but is essential and sufficient for the induction of some O-3-dependent pathways. This hypothesis was tested resolving the time course of O-3-induced transcript accumulation of alternative oxidase (AOX1a), glutathione peroxidase (GPX), aminocyclopropancarboxylic acid synthase (ACS2) that is critical for the synthesis of ethylene, phenylalanine ammonia lyase (PALa) and the pathogenesis-related protein PR1a. The data show that early O-3 and NO caused transcriptional activation of the scavenger encoding proteins AOX1a, GPX and the induction of ethylene production through ACS2 are cGMP independent. By contrast, the early response of PALa and the late response of PR1a show critical dependence on cGMP. New Phytologist (2009) 181: 860-870doi: 10.1111/j.1469-8137.2008.02711.x.