Role of Phytochromes in Shade Avoidance Ecophysiological and Molecular aspects

1. Plant Biology MSc course Plants and their Environment 2007 I: Abiotic interactions Thijs Pons and Marcel Proveniers Role ofPhytochromesin Shade AvoidanceEcophysiological and Molecular aspects

2. Light as source of: • Energy - for photo-autotrophic growth • Information – maximize/optimize resource acquisition Shade Avoidance in (shade avoiding) plants: Avoidance of shade by neighbors in time and space by adjustment of growth and development that optimizes light capture for photosynthetic utilization (and may suppress light capture by neighbors)

3. Perception of the light climate

4. Photoreceptors in the life cycle

5. Phytochromes, involvement in shade avoidance during the life cycle

6. In this part of the course we will investigate the role of Phytochromes in different aspects of shade avoidance • Significance in a Plant’s life cycle • Physiological characterization of the process • Which phytochromes are involved in perception and signal transduction • Interaction with other photoreceptors, other signaling • mechanisms and phytohormones • Transcription under phytochrome control • Downstream molecular processes

7. Organization the course MSc course Plants and their Environment Part I: Abiotic interactions • Monday 23 April • Short introduction by lecturers • Distribution of topics for preparation of presentations • Private Study: • Preparation of presentations • Study of the subject of other presentations • Write Essay • Tuesday 1 & Thursday 3 May • Presentations of selected topics • Discussions chaired by other students from the group • Tuesday 8 May • Hand in Essay that describes in your own words the main topics that were discussed.

8. Phytochrome spectra synthesis Physiological action • R:FR • PFD 655-665 nm • PFD 725-735 nm • open: 1.2 • canopy: 0.2 • Pfr/P: • open: 0.6 • canopy: 0.1 • R: 0.8 • FR: 0.02 Labile phytochrome phyA type II (seedling phytochrome) Stable phytochrome phyB (+C, D, E) type I (seed phytochrome) Smith 2000

9. Red – Farred reversibilityan indication that phytochroom is involved

10. Light responses in seeds Relative importance of the 3 response types is very different between species and history of the seed Lactuca sativa (lettuce seeds) The three response types are also observed in seedlings Pons, 2000 VLFR = Very Low Fluence Response (phyA). a low concentration of Pfr breaks dormancy LFR = Low Fluence Response (phyB) a higher threshold value of Pfr is required for dormancy breaking HIR = High Irradiance Response irradiation of long duration inhibits germination; effect increases with increasing irradiance FR-HIR most effective at 710 – 720 nm and low R:FR (phyA) R-HIR most effective in red and white light (phyB in seedlings)

11. Germination in the soil and on the surface VLFR Exposure of the weed seed population to light during soil cultivation Scopel et al. 94

12. Canopy shade Germination of Plantago major Pons 2000

13. Shade avoidance in seeds • Avoidance of germination at a time when the resulting seedling • would be subject to competition from established plants • Dormancy enforced by darkness in soil. • Breaking of dormancy by short exposure to light during disturbance. • Functional significance: • Germination is delayed until after a disturbance event. • - Dormancy enforced by canopy shade light (low R:FR) • Functional significance: • - Germination is delayed until an opening in the leaf canopy is created • typically by a disturbance event. • - Dormancy is enforced until the seed is buried in the soil and darkness • maintains dormancy further.

14. Shade avoidance in vegetative plants Light environment in leaf canopies Lysimachia vulgaris different canopy densities

15. Nicotiana Arabidopsis High Light Spectral Shade Vegetative developmentshade avoidance in leaf canopies Low High canopy density • Petiole hyponasty • Petiole elongation • Internode elongation • Leaf Senescence Boonman 06 Pierik et al. 2005

16. Spectral and neutral shade effects Arabidopsis High Light Spectrally Neutral Shade erect creeping stem stoloniferous Low R:FR Huber et al. 1996 Pierik et al. 2005

17. Adapted from H. Smith R:FR effects independent of PARChenopodium a shade avoiding species

18. Reflected light FR absorbed by stems increases with increasing LAI before PAR (R & B) incident on the leaves decreases. This triggers internode elongation and a phototropic response under control of phytochrome. FR R &B Ballare 99

19. Wt phyB Use of phy mutants Mutants lacking phyB have a constitutive shade avoidance phenotype. Long petioles, long internodes, low chlorophyll, early flowering; phyA resembles very much the wild type. This means that the spectrally sensitive component of shade avoidance is largely under control of phyB. There are also other phytochromes involved.

20. Photomorphogenesis under control of phytochrome in vegetative plants • Shade avoidance - largely under control of phyB • Functional significance: Maximize capture of light • and its photosynthetic utilization when • similar-sized plants compete for light. • (shade tolerant species do not show • a pronounced shade avoidance response)

21. Topics for literature discussions on Involvement of Phytochrome in shade avoidance in seeds and vegetative plants Seeds (tuesday 1 May) 1. Role of different phytochromes in Arabidopsis Shinomura et al. (1994), Botto et al. (1996), Hennig et al. (2002) 2. Role of different phytochromes in Tomato Sinchijo et al. (2001), Appenroth et al. (2006) 3. Interaction between light and temperature effects Donohue et al. (2007), Penfield et al. (2005) 4. Downstream regulation Oh et al. (2004), Oh et al. (2006) Vegetative Plants (thursday 3 may) 5. Role of different phytochromes 1 Devlin et al. (1996), Devlin et al. (1998) 6. Role of different phytochromes 2 Devlin et al. (1999), Franklin et al. (2003) 7. Regulation of gene expression Salter et al. (2003), Sessa et al. (2005) 8. Primary target genes Devlin et al. (2003), Roig-Villanova et al. (2006)