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Homework #1 is posted and due 9/17 Bonus #1 is posted and due 10/24 Discussions started this week Why so many steps? Multiple steps allow for signal specificity. Different relay molecules lead to different responses Multiple steps allow for signal amplification: Calcium is a simple method of amplifying signals Calcium is a common effector. Cytoplasmic calcium levels are normally low. During signal transduction, calcium can be released into the cytoplasm: Perception During signal transduction, calcium can be released into the cytoplasm: Transduction During signal transduction, calcium can be released into the cytoplasm: Response During signal transduction, calcium can be released into the cytoplasm General model of Ca++ signaling General model of Ca++ signaling Multiple steps allow for signal amplification: Calcium is a simple method of amplifying signals Ca++ is involved in many responses Ca++ is involved in signal transduction for responses of: • • • • • • • • • in Plants in Animals Development • Neurons Cold • Muscle movement Guard cell closing • Wounding Osmotic shock • Development Light • Fertilization Fungal infection • Hormones Touch • … Pollen tube growth Wounding… How can there be specificity? Everything has its place… Some Ca++ channels have specific effectors associated with them: Micro-domains Ikeda, Science 12 Oct 2001 Vol 294:318-319 Root nodules: Nitrogen fixation Bacteria and Plants Symbiosis Signaling between bacteria and plants 1nM Nod Fig 3. Shaw and Long, Plant Physiology, March 2003, Vol. 131, pp. 976–984 10nM Nod A biphasic Ca++ response to Nod factor: 1nM Nod - toward nucleus 10nm Nod - away from nucleus 1nM Nod 10nM Nod 1nM Nod 10nM Nod A biphasic Ca++ response to Nod factor: 1nM Nod - toward nucleus 10nm Nod - away from nucleus Fig 3. Shaw and Long, Plant Physiology, March 2003, Vol. 131, pp. 976–984 Everything has its place… 2 hypotheses about how Ca++ signals are transduced: Signatures vs. Switches Fig 1. Scrase-Field and Knight, Current Opinion in Plant Biology 2003, 6:500–506 Photosynthesis: Plants can make sugar using energy from the sun, water from the ground, and CO2 from the air. Stomata regulate gas exchange: CO2 in, O2 and water out H2 O H2 O Stomata open closed Opening and closing of stomata Ca++ fluxes in guard cells in response to hormone or stress that cause stomatal closing. Wildtype vs. det3 and gca2: mutants that fail to close stomata following treatment Fig 5. Sanders et al., The Plant Cell, S401–S417, Supplement 2002 2 hypotheses about how calcium signals are transduced: Signatures vs. Switches Fig 1. Scrase-Field and Knight, Current Opinion in Plant Biology 2003, 6:500–506 Signal Transduction External Stimulus Internal Effector… Effector Effector Effector Response Perception (by receptor) Stimulus Homework #1 is posted and due 9/17 Bonus #1 is posted and due 10/24 Discussions started this week