(Summer sun) light and plant health

Our PhD students are organizing the European Plant Science Retreat here in Utrecht. We’re lucky, it’s fabulous sunny weather, Utrecht at its best. The organizers have done a fantastic job and invited amazing speakers, which even allowed me to catch up with friends and colleagues Carlos Ballaré and Amy Austin. After a joyful lunch yesterday with the four of us (my love, Christa Testerink, is also a keynote, great planning indeed!), I attended Carlos’ talk today on light quality-dependent modulation of plant immunity. This is a topic we share an interest in (Ballaré et al., 2012) and that Carlos Ballaré has been pioneering.  I think it deserves more attention:

The Ballaré lab published quite some years ago that plants that get exposed to light that is enriched with Far-red light reflected by proximate neighbors, not only activate the long established shade avoidance responses (e.g. Ballaré & Pierik, Plant Cell Env., 2017; Fiorucci & Fankhauser, Curr.Opin.Plant Biol., 2017), but also suppress resistance against herbivorous insects (Izaguirre et al., PNAS, 2006; Moreno et al., PNAS, 2009). This sparked many people’s interest of course, including ours. The Ballaré lab as well as ours showed how also defense against necrotrophic pathogenic fungi, such as Botrytis, is suppressed (Cerrudo et al., Plant Physiol., 2012), and this extends to a biotrophic bacterium (de Wit et al., Plant J., 2013).  This trade-off is clearly controlled by plants and not just passive, and although parts of the mechanisms have been identified, quite a bit is still to be resolved. Shortly, active phytochrome promotes stability of DELLA proteins, which are growth suppressors and defense activators via their negative effect on JAZ protein activity. In shade, inactive phytochrome results in DELLA degradation and may also directly affect JAZ abundance to desensitize plants to jasmonate (JA). For a great overview of these pathway interactions, check out this review: Ballaré, Ann. Rev. Plant Biol., 2014.

Although the mechanistic work is done mostly in Arabidopsis, the interaction has been found now in a very wide panel of species including tobacco, tomato (both Izaguirre et al., PNAS, 2006), Arabidopsis (Moreno et al., PNAS, 2009de Wit et al., Plant J., 2013), passionfruit (Izaguirre et al., Oecologia, 2013) and more. Are all plants showing this light-defense interaction? We don’t think so. Our former PhD student Lot Gommers observed that a wild Geranium from forest understories, Geranium robertianum, does not show shade avoidance in response to FR-enrichment and does also not down regulate it’s immunity against Botrytis (Gommers et al., Plant Cell, 2017).
Some of these are strong emitters of Volatile Organic Compounds (VOCs) and indeed VOC emission, both JA-dependent and JA-independent, are strongly affected by FR light enrichment (Kegge et al., New Phytol., 2013; Cortes et al., New Phytol., 2016).  As a consequence, indirect plant defenses are affected, and we will probably be seeing more about this in the future.

Sarah Courbier is a PhD student in my group, studying FR-modulation of immunity in tomato under different light quality regimes. We are in a consortium studying how LED lighting can be implemented in greenhouse cultivation of tomato in order to save energy. We hope to identify how this can be used to optimize various aspects of plant life that contribute to yield, including disease resistance.  The ambition is to save electricity and increase tomato crop yield simultaneously, using and furthering scientific research.

References
Ballaré, 2014: doi.org/…46/annurev-arplant-050213-040145
Ballaré et al., Plant Physiol., 2012: doi.org/10.1104/pp.112.200733
Ballaré & Pierik, Plant Cell Env., 2017: doi.org/10.1111/pce.12914
Cerrudo et al., 2012: doi.org/10.1104/pp.112.193359
Cortes et al, 2016: doi: 10.1111/nph.14210
Fiorucci & Fankhauser, 2017: doi.org/10.1016/j.cub.2017.05.085
Gommers et al., 2017: doi.org/10.1105/tpc.16.00790
Izaguirre et al., 2006: doi.org/10.1073/pnas.0509805103
Izaguirre et al., 2013: DOI 10.1007/s00442-013-2721-9
Kegge et al, 2013: doi.org/10.1111/nph.12407
Moreno et al., 2009: doi.org/10.1073/pnas.0900701106
de Wit et al., 2013: doi.org/10.1111/tpj.12203

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