The Plant Cell, Vol. 26: 1833, May 2014, www.plantcell.org ã 2014 American Society of Plant Biologists. All rights reserved.
IN BRIEF
Living in the Shadows: How Plants Balance Growth and Jasmonate-Dependent Defense Responses in the Shade No wonder the plants in my vegetable garden come down with every disease known to the plant kingdom; they don’t get enough sun! Shady conditions trigger a suite of responses that are all too familiar, including stem and petiole elongation, upward bending of leaves, early flowering, and reduced disease resistance. In the forest, the red/far red (R/FR) light ratio decreases due to the absorption of R light by plants in the canopy layer. In the understory, this light shift is detected by photoreceptors such as phytochrome B (phyB), causing these plants to ratchet up their growth in an attempt to outcompete their neighbors, which leaves fewer resources available for defense. However, since disease vectors lurk in shady as well as sunny locations, this balance of resources has to be finely tuned. Many plant defense responses are mediated by the phytohormone jasmonate (JA). Inactivation of phyB by low R/FR ratios somehow promotes a reduction in the plant’s sensitivity to JA and JA-dependent defense gene expression, lowering its resistance to insect herbivory and necrotrophic pathogens (de Wit et al., 2013). However, the molecular mechanism underlying the complex response of plants to shade conditions remains unclear. Several transcription factors (TFs) that activate various JA-mediated responses have been identified, including MYC2, MYC3, and MYC4. Under basal conditions, JAZ repressors block the activity of these TFs, while increased JA levels lead to the degradation of JAZ repressors by the 26S proteasome. This, in turn, activates the MYC TFs, unleashing JA-mediated responses. Such responses are only now coming into focus. For example, Ferna´ndez-Calvo et al. (2011) showed that MYC2, MYC3, and MYC4 are involved in the activation of JAmediated defense responses to herbivory. Chico et al. (pages 1967–1980) go one step further, showing that these TFs are also required for JA-mediated defenses against the necrotrophic pathogen Botrytis cinerea.
www.plantcell.org/cgi/doi/10.1105/tpc.114.127332
In this important study, the authors also uncover a mechanism underlying the regulation of these TFs and their JAZ repressors by light quality, bridging the gap in our understanding of how shade represses JAmediated disease resistance. The authors analyzed the expression of MYC2, MYC3, and MYC4 fused to green fluorescent protein in transgenic Arabidopsis thaliana plants in the presence of a translational inhibitor, revealing that these TFs are short-lived and regulated through proteasomal degradation. JA stabilizes these proteins, while dark and FR treatment lead to their degradation; JA treatment only partially restores this dark-induced destabilization. In addition, mutant analysis indicated that light-activated phyB is required for MYC2 stability. Moreover, while wild-type plants exhibit increased susceptibility to B. cinerea
in simulated shade, as expected, the myc2 myc3 myc4 mutant is susceptible to this pathogen under both white light and shade conditions (see figure). Therefore, MYC2, MYC3, and MYC4 mediate JA-mediated defenses against B. cinerea, and shadetriggered susceptibility is likely achieved by FR-mediated inactivation of these TFs. In the shade, although pathogen attack triggers the production of JA, plants only partially regain their ability to fight back, as the restoration of the MYC TFs is limited, and plant defenses are therefore weakened. The authors also determined that simulated shade increases the abundance of JAZ repressors, adding another detail to the complex molecular mechanism underlying the shade response and giving me another reason to grow ferns instead of shade-intolerant vegetables.
Jennifer Lockhart Science Editor [email protected] ORCID ID: 0000-0002-1394-8947
REFERENCES
The effect of shade on JA-mediated defenses against pathogens. Simulated shade (FR-enriched white light [WL]) increases the susceptibility of wild-type plants to B. cinerea, while the triple myc2 myc3 myc4 mutant is similarly susceptible under basal and shade conditions. (Figure courtesy of R. Solano.)
Chico, J.M., Ferna´ndez-Barbero, G., Chini, A., Ferna´ ndez-Calvo, P., Dı´ ez-Dı´ az, M., and Solano, R. (2014). Repression of jasmonatedependent defenses by shade involves differential regulation of protein stability of MYC transcription factors and their JAZ repressors in Arabidopsis. Plant Cell 26: 1967–1980. de Wit, M., Spoel, S.H., Sanchez-Perez, G.F., Gommers, C.M., Pieterse, C.M., Voesenek, L.A., and Pierik, R. (2013). Perception of low red:far-red ratio compromises both salicylic acid- and jasmonic acid-dependent pathogen defences in Arabidopsis. Plant J. 75: 90–103. Ferna´ndez-Calvo, P., et al. (2011). The Arabidopsis bHLH transcription factors MYC3 and MYC4 are targets of JAZ repressors and act additively with MYC2 in the activation of jasmonate responses. Plant Cell 23: 701– 715.
Living in the Shadows: How Plants Balance Growth and Jasmonate-Dependent Defense Responses in the Shade Jennifer Lockhart Plant Cell 2014;26;1833; originally published online May 13, 2014; DOI 10.1105/tpc.114.127332 This information is current as of May 1, 2015 References
This article cites 3 articles, 2 of which can be accessed free at: http://www.plantcell.org/content/26/5/1833.full.html#ref-list-1
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IN BRIEF
Living in the Shadows: How Plants Balance Growth and Jasmonate-Dependent Defense Responses in the Shade No wonder the plants in my vegetable garden come down with every disease known to the plant kingdom; they don’t get enough sun! Shady conditions trigger a suite of responses that are all too familiar, including stem and petiole elongation, upward bending of leaves, early flowering, and reduced disease resistance. In the forest, the red/far red (R/FR) light ratio decreases due to the absorption of R light by plants in the canopy layer. In the understory, this light shift is detected by photoreceptors such as phytochrome B (phyB), causing these plants to ratchet up their growth in an attempt to outcompete their neighbors, which leaves fewer resources available for defense. However, since disease vectors lurk in shady as well as sunny locations, this balance of resources has to be finely tuned. Many plant defense responses are mediated by the phytohormone jasmonate (JA). Inactivation of phyB by low R/FR ratios somehow promotes a reduction in the plant’s sensitivity to JA and JA-dependent defense gene expression, lowering its resistance to insect herbivory and necrotrophic pathogens (de Wit et al., 2013). However, the molecular mechanism underlying the complex response of plants to shade conditions remains unclear. Several transcription factors (TFs) that activate various JA-mediated responses have been identified, including MYC2, MYC3, and MYC4. Under basal conditions, JAZ repressors block the activity of these TFs, while increased JA levels lead to the degradation of JAZ repressors by the 26S proteasome. This, in turn, activates the MYC TFs, unleashing JA-mediated responses. Such responses are only now coming into focus. For example, Ferna´ndez-Calvo et al. (2011) showed that MYC2, MYC3, and MYC4 are involved in the activation of JAmediated defense responses to herbivory. Chico et al. (pages 1967–1980) go one step further, showing that these TFs are also required for JA-mediated defenses against the necrotrophic pathogen Botrytis cinerea.
www.plantcell.org/cgi/doi/10.1105/tpc.114.127332
In this important study, the authors also uncover a mechanism underlying the regulation of these TFs and their JAZ repressors by light quality, bridging the gap in our understanding of how shade represses JAmediated disease resistance. The authors analyzed the expression of MYC2, MYC3, and MYC4 fused to green fluorescent protein in transgenic Arabidopsis thaliana plants in the presence of a translational inhibitor, revealing that these TFs are short-lived and regulated through proteasomal degradation. JA stabilizes these proteins, while dark and FR treatment lead to their degradation; JA treatment only partially restores this dark-induced destabilization. In addition, mutant analysis indicated that light-activated phyB is required for MYC2 stability. Moreover, while wild-type plants exhibit increased susceptibility to B. cinerea
in simulated shade, as expected, the myc2 myc3 myc4 mutant is susceptible to this pathogen under both white light and shade conditions (see figure). Therefore, MYC2, MYC3, and MYC4 mediate JA-mediated defenses against B. cinerea, and shadetriggered susceptibility is likely achieved by FR-mediated inactivation of these TFs. In the shade, although pathogen attack triggers the production of JA, plants only partially regain their ability to fight back, as the restoration of the MYC TFs is limited, and plant defenses are therefore weakened. The authors also determined that simulated shade increases the abundance of JAZ repressors, adding another detail to the complex molecular mechanism underlying the shade response and giving me another reason to grow ferns instead of shade-intolerant vegetables.
Jennifer Lockhart Science Editor [email protected] ORCID ID: 0000-0002-1394-8947
REFERENCES
The effect of shade on JA-mediated defenses against pathogens. Simulated shade (FR-enriched white light [WL]) increases the susceptibility of wild-type plants to B. cinerea, while the triple myc2 myc3 myc4 mutant is similarly susceptible under basal and shade conditions. (Figure courtesy of R. Solano.)
Chico, J.M., Ferna´ndez-Barbero, G., Chini, A., Ferna´ ndez-Calvo, P., Dı´ ez-Dı´ az, M., and Solano, R. (2014). Repression of jasmonatedependent defenses by shade involves differential regulation of protein stability of MYC transcription factors and their JAZ repressors in Arabidopsis. Plant Cell 26: 1967–1980. de Wit, M., Spoel, S.H., Sanchez-Perez, G.F., Gommers, C.M., Pieterse, C.M., Voesenek, L.A., and Pierik, R. (2013). Perception of low red:far-red ratio compromises both salicylic acid- and jasmonic acid-dependent pathogen defences in Arabidopsis. Plant J. 75: 90–103. Ferna´ndez-Calvo, P., et al. (2011). The Arabidopsis bHLH transcription factors MYC3 and MYC4 are targets of JAZ repressors and act additively with MYC2 in the activation of jasmonate responses. Plant Cell 23: 701– 715.
Living in the Shadows: How Plants Balance Growth and Jasmonate-Dependent Defense Responses in the Shade Jennifer Lockhart Plant Cell 2014;26;1833; originally published online May 13, 2014; DOI 10.1105/tpc.114.127332 This information is current as of May 1, 2015 References
This article cites 3 articles, 2 of which can be accessed free at: http://www.plantcell.org/content/26/5/1833.full.html#ref-list-1
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© American Society of Plant Biologists ADVANCING THE SCIENCE OF PLANT BIOLOGY
