Plant Growth Regulators and Hormones: Dissecting the Secrets of Plant Development

1. Help needed for dissecting frogs with 7th graders on Friday April 5 • 8:30- 10:30 in CSC220

2. Next Presentation = GMO or Gene-edited plants • Friday April 12 • GMO • Herbicide resistance • Pathogen/herbivore resistance • Improving nutrition (biofortification) • Improving shelf-life • Making vaccines, other useful biochems • Changing flower colors • Gene-edited • Targeted disruptions • Targeted improvements

3. Growth regulators All are small organics: made in one part, affect another part Treating a plant tissue with a hormone is like putting a dime in a vending machine. It depends on the machine, not the dime!

4. ABA Counteracts GA effects • Causes seed dormancy & inhibits seed germination • Inhibits fruit ripening

5. ABA Synthesized during seed maturation to promote dormancy Also closes stomates in stress by opening Ca then closing K channels Induces many genes (~10% of total) via several different mechs • bZIP/ABRE (ABI3, 4, 5 + AREBs) • MYC/MYB

6. Schroeder version of ABA signaling • PYR/PYL/RCAR is key player • Binds ABA& inactivates PP2C • Allows SnRK2 to function • SnRK2 then kinases many targets, including ion channels, TFs & ROS producers

7. Ethylene A gas that acts as a hormone! Chinese burned incense to ripen pears 1864: leaks from street lamps damage trees Neljubow (1901): ethylene causes triple response: short stems, swelling & abnormal horizontal growth

8. Ethylene Signaling • In absence of ethylene, receptors activate CTR1 which represses EIN2-dependent signaling • Upon binding ethylene, receptors inactivate CTR1 by unknown mech 3. Active EIN2 activates EIN3 4. EIN3 turns on genes needed for ethylene response. 5. Ethylene receptor also turns off EIN3 degradation

9. Brassinosteroids First identified in pollen from Brassicas (= brassins) • Stimulate both elongation and cell division • At low [] induce elongation • At high [] induce division • Assayed with bean stems or rice lamina • Purified 4 mg from 227 kg of bee-collected pollen & determined structure by X-ray crystallography

10. Brassinosteroids • Active receptor kinases BSK • BSK activates BSU • BSU dephosphorylates BIN2 -> gets destroyed • BES1/BIM activates genes • BZR1 activates a different set, and represses BR synthesis

11. Brassinosteroids & other growth regulators • These gene products create BR responses • Note overlap with Auxin! • - interaction with ABA, eg in seed germination • - interaction with ethylene & IAA transport in apical hook • Promote skotomorphogenesis: BR mutants have COP phenotype. • - interaction with jasmonate I in inhibition of root growth

12. Strigolactones • Growth regulators derived from carotenoids • Released from roots to attract endomycorrhizae • trigger germination of parasitic • plants, e.g. witchweed (Strigaasiatica)

13. Strigolactones • Growth regulators derived from carotenoids • Interact with auxin to inhibit shoot branching • Synthesized in response to P or N starvation • increase lateral roots and root hairs & attract symbionts

14. Strigolactones • Growth regulators derived from carotenoids • Interact with auxin to inhibit shoot branching • Synthesized in response to P or N starvation • increase lateral roots and root hairs & attract symbionts • Trigger degradation of proteins that stimulate branching by an E3 ligase

15. Strigolactones • Growth regulators derived from carotenoids • Trigger degradation of proteins that stimulate branching by an E3 ligase • Trigger degradation of SMAX1 via MAX2 E3 receptor • Allows seed germination, seedling growth & development • Link with karrikin signaling

16. Karrikins • Growth regulators derived from carbohydrates by burning • Stimulate germination of dormant seeds waiting for fire • Trigger degradation of SMAX1 via MAX2 E3 receptor • Allows seed germination, seedling growth & development

17. Jasmonates Fatty acid derivatives first discovered as growth inhibitors made by a fungus

18. Jasmonates Fatty acid derivatives first discovered as growth inhibitors made by a fungus • Subsequently found to be made by plants in response to stress

19. Jasmonates Fatty acid derivatives mainly involved in stress signaling • Also needed for pollen development • Maturation • Elongation of stamen filaments • Dehiscence of anther locules

20. Jasmonates Fatty acid derivatives mainly involved in stress signaling • Also needed for pollen development • JAZ proteins block TF until bind JA

21. Jasmonates Fatty acid derivatives mainly involved in stress signaling • Also needed for pollen development • JAZ proteins block TF until bind JA • Degraded when JA is present • COI1 = E3 receptor for JAZ

22. Jasmonates Fatty acid derivatives mainly involved in stress signaling • Also needed for pollen development • JAZ proteins block TF until bind JA • Degraded when JA is present • COI1 = E3 receptor for JAZ • JA genes are transcribed • Control pollen development & other cellular effects

23. Jasmonates Fatty acid derivatives mainly involved in stress signaling • Also needed for pollen development • JAZ proteins block TF until bind JA • Degraded when JA is present • COI1 = E3 receptor for JAZ • JA genes are transcribed • Control pollen development & other cellular effects, including trichome development

24. Jasmonic Acid • Jasmonic Acid and Ethylene induce an overlapping set of defenses

25. Salicylic Acid Affects plant growth and development

26. Salicylic Acid Affects plant growth and development • photosynthesis

27. Salicylic Acid Affects plant growth and development • Photosynthesis • transpiration

28. Salicylic Acid Affects plant growth and development • Photosynthesis • Transpiration • ion uptake and transport

29. Salicylic Acid Affects plant growth and development • Photosynthesis • Transpiration • ion uptake and transport Best characterised role is in systemic acquired resistance

30. Salicylic Acid Affects plant growth and development • Photosynthesis • Transpiration • ion uptake and transport Best characterised role is in systemic acquired resistance

31. Salicylic Acid Best characterised role is in systemic acquired resistance • Whole plant response following exposure to a pathogen

32. Salicylic Acid Best characterised role is in systemic acquired resistance • Whole plant response following exposure to a pathogen

33. Salicylic Acid Best characterised role is in systemic acquired resistance • Whole plant response following exposure to a pathogen • Necrotic lesion releases phloem-mobile signal inducing Sa in target (could be methyl-SA or a lipid)

34. Salicylic Acid Best characterised role is in systemic acquired resistance • Whole plant response following exposure to a pathogen • Necrotic lesion releases phloem-mobile signal inducing Sa in target (could be methyl-SA or a lipid) • SA induces expression of defense proteins via NPR1

35. Salicylic Acid • SA induces expression of defense proteins via NPR1 • Some overlap with Ethylene and Jasmonic Acid responses

36. Nitric Oxide • Affects many aspects of plant life cycle • Primarily made in response to stress • Inhibits respiration under anoxia • Enhances tolerance of many stresses

37. Nitric Oxide • Affects many aspects of plant life cycle • Primarily made in response to stress • Inhibits respiration under anoxia • Enhances tolerance of many stresses • Made at least 6 different ways

38. Nitric Oxide Figuring out signaling mechs is ongoing, involves multiple processes

39. Nitric Oxide Figuring out signaling mechs is ongoing, involves multiple processes • In germination appears to up-regulate ABA destruction

40. Nitric Oxide • Figuring out signaling mechs is ongoing, involves multiple processes • In germination appears to up-regulate ABA destruction • In guard cells is signaling intermediate • Triggers degradation of Ethylene • response factors

41. Nitric Oxide Figuring out signaling mechs is ongoing, involves multiple processes • In germination appears to up-regulate ABA destruction • In guard cells is signaling intermediate • Triggers degradation of Ethylene-response factors

42. Peptides • Systemins • 18 aa peptides released in response to herbivory

43. Peptides • Systemins • 18 aa peptides released in response to herbivory

44. Peptides • Systemins • 18 aa peptides released in response to herbivory • Trigger synthesis of jasmonic acid & ethylene in target cells

45. Peptides • Systemins • 18 aa peptides released in response to herbivory • Triggers synthesis of jasmonic acid & ethylene in target cells • Some attract parasitoids

46. Peptides • Systemins • 18 aa peptides released in response to herbivory • Trigger synthesis of jasmonic acid & ethylene in target cells • Activate defense genes

47. Peptides • Systemin • 18 aa peptide released in response to herbivory • Triggers synthesis of jasmonic acid & ethylene in target cells • Activates defense genes • hydroxyproline-rich glycopeptides • Unrelated structures, but similar size and also activate JA

48. Other Peptides • Clavata 3-Wuschel signaling • WUSCHEL is a transcription factor made in the “Organizing Center” of the shoot apical meristem • Promotes stem cell formation

49. Other Peptides • Clavata 3-Wuschel signaling • WUSCHEL is a transcription factor made in the “Organizing Center” of the shoot apical meristem • Promotes stem cell formation • Is secreted and taken up by cells above it, where it induces expression of Clavata 3 which is only made in a few cells of the SAM and promotes differentiation

50. Clavata 3-Wuschel signaling • Clavata 3 which is only made in a few cells of the SAM and promotes differentiation • Is secreted and represses WUSCHEL expression in underlying cells • This feedback loop controls size of the apical meristem