Arabidopsis MAP kinase phosphatase 1 and its target MAP kinases 3 and 6 antagonistically determine UV‐B stress tolerance, independent of the UVR8 photoreceptor pathway

Abstract

SUMMARYPlants perceive UV-B radiation as an informational signal by a pathway involving UVR8 as UV-B photoreceptor, activating photomorphogenic and acclimation responses. In contrast, the response to UV-B as an environmental stress involves mitogen-activated protein kinase (MAPK) signalling cascades. Whereas the perception pathway is plant specific, the UV-B stress pathway is more broadly conserved. Knowledge of the UV-B stressactivated MAPK signalling pathway in plants is limited, and its potential interplay with the UVR8-mediated pathway has not been defined. Here, we show that loss of MAP kinase phosphatase 1 in the mutant mkp1 results in hypersensitivity to acute UV-B stress, but without impairing UV-B acclimation. The MKP1-interacting proteins MPK3 and MPK6 are activated by UV-B stress and are hyperactivated in mkp1. Moreover, mutants mpk3 and mpk6 exhibit elevated UV-B tolerance and partially suppress the UV-B hypersensitivity of mkp1. We show further that the MKP1-regulated stress-response MAPK pathway is independent of the UVR8 photoreceptor, but that MKP1 also contributes to survival under simulated sunlight. We conclude that, whereas UVR8-mediated acclimation in plants promotes UV-B-induced defence measures, MKP1-regulated stress signalling results when UV-B protection and repair are insufficient and damage occurs. The combined activity of these two mechanisms is crucial to UV-B tolerance in plants.

Arabidopsis thaliana natural variation reveals connections between UV radiation stress and plant pathogen-like defense responses

“…Based on earlier observations, using three Arabidopsis natural strains Col-0, C24 and Ws-2, this was expected to induce UV stress and cause damage to plant tissues (Kalbina and Strid, 2006;Jenkins, 2009;Hideg et al, 2013). Indeed, we observed a strong transcriptional activation of UV stress markers WRKY30 and PR5 in six accessions with contrasting phenotypes (Supplementary Table 7), indicating extensive production of reactive oxygen species (ROS) and activation of defense responses (Kalbina and Strid, 2006;Jenkins, 2009).…”

“…In order to provide more specificity to this screen, we selected candidates with e.g. high amplitude fold-changes, transcriptional dependency on UVR8 and/or HY5 (Brown et al, 2005;Oravecz et al, 2006;Kilian et al, 2007;Lee et al, 2007;Gonz alez Besteiro et al, 2011;Obayashi et al, 2011) and/or overlapping with lower association peaks in our GWA studies. Combination of these criteria together with mutant availability in major public collections reduced our screening population to 50 T-DNA insertion mutant lines, out of which 45 could be propagated and obtained as homozygous lines (Supplementary Table 2).…”

“…This was expected to induce UV stress and cause damage to plant tissues (Kalbina and Strid, 2006;Jenkins, 2009;Hideg et al, 2013). Subsequently, three growth related traits: leaf length (defined as median of the five longest leaves), leaf area and fresh aerial biomass were scored.…”

UV-B-induced photomorphogenesis in Arabidopsis

“…These responses are mediated by a recently characterized photoreceptor UV RESISTANCE LOCUS 8 (UVR8), and are required for plants' acclimation to UV-B stress (Ulm and Nagy, 2005;Jenkins, 2009;Rizzini et al, 2011). It was shown recently that the two pathways are largely independent of each other, but both are important for plants to achieve full UV-B tolerance (Gonzalez Besteiro et al, 2011). However, it should be noted that there is substantial overlap in the fl uence rates that initiate the different types of responses (Jenkins, 2009).…”

Footprints of the sun: memory of UV and light stress in plants

“…For example, different groups of UV-B response genes are still represented in uvr8 , cop1 , hy5 mutants upon UV-B radiation (Brown et al, 2005; Brown and Jenkins, 2008; Lang-Mladek et al, 2012). Mitogen-activated protein kinase (MAPK) signaling cascades have been proposed to be involved in high dose UV-B stress independently of UVR8-mediated UV-B signaling (Ulm et al, 2002; Gonzalez Besteiro et al, 2011). Arabidopsis plants with loss of MAP kinase phosphatase 1 ( mkp1 ) function are hypersensitive to acute UV-B radiation, but without showing impairment to UV-B acclimation.…”