Faculté des sciences

Light regulation and daytime dependency of inducible plant defences in Arabidopsis: phytochrome signalling controls systemic acquired resistance rather than local defence

Griebel, Thomas ; Zeier, Jürgen

In: Plant Physiology, 2008, vol. 147, p. 790-801

We have examined molecular and physiological principles underlying the light-dependency of defence activation in Arabidopsis plants challenged with the bacterial pathogen Pseudomonas syringae. Within a fixed light/dark cycle, plant defence responses and disease resistance significantly depend on the time of day when pathogen contact takes place. Morning and midday inoculations result in... Plus

Ajouter à la liste personnelle
    Summary
    We have examined molecular and physiological principles underlying the light-dependency of defence activation in Arabidopsis plants challenged with the bacterial pathogen Pseudomonas syringae. Within a fixed light/dark cycle, plant defence responses and disease resistance significantly depend on the time of day when pathogen contact takes place. Morning and midday inoculations result in higher salicylic acid (SA) accumulation, faster expression of pathogenesis-related (PR) genes, and a more pronounced hypersensitive response than inoculations in the evening or at night. Rather than to the plants' circadian rhythm, this increased plant defence capability upon day inoculations is attributable to the availability of a prolonged light period during the early plant-pathogen interaction. Moreover, pathogen responses of Arabidopsis double mutants affected in light perception, i.e. cryptochrome1cryptochrome2 (cry1cry2), phototropin1phototropin2 (phot1phot2), and phytochromeAphyto-chromeB (phyAphyB) were assessed. Induction of defence responses by either avirulent or virulent P. syringae at inoculation sites is relatively robust in leaves of photoreceptor mutants, indicating little cross-talk between local defence and light signalling. In addition, the blue-light receptor mutants cry1cry2 and phot1phot2 are both capable to establish a full systemic acquired resistance (SAR) response. Induction of SAR and SA-dependent systemic defence reactions, however, are compromised in phyAphyB mutants. Phytochrome regulation of SAR involves the essential SAR component FLAVIN-DEPENDENT MONOOXYGENASE 1 (FMO1). Our findings highlight the importance of phytochrome photoperception during systemic rather than local resistance induction. The phytochrome system seems to accommodate the supply of light energy to the energetically costly increase in whole plant resistance.