Growth regulators Auxins Cytokinins Gibberellins Abscisic Acid Ethylene Brassinoteroids

1. Growth regulators Auxins Cytokinins Gibberellins Abscisic Acid Ethylene Brassinoteroids Jasmonic Acid Salicylic Acid Strigolactones Nitric Oxide Sugars

2. 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

3. 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

4. Brassinosteroids • Validated by mutants • BR synthesis mutants are dwarf & defective • rescued by BR • BR-insensitive mutants are dwarf & defective • don’t respond to BR

5. 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

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

7. 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

8. 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

9. 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

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

11. 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

12. Salicylic Acid • SA induces expression of defense proteins via NPR1 • Ethylene and Jasmonic Acid induce an overlapping set of defenses

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

14. 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

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

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

17. 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

18. 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

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

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

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

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

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

24. 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

25. 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

26. 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

27. 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

28. Clavata 3-Wuschel signaling • Clavata 3 which is only made in a few cells of the SAM and promotes differentiation • This feedback loop controls size of the apical meristem • Acts via at least 4 different receptor protein kinases

29. Clavata 3-Wuschel signaling • Clavata 3 which is only made in a few cells of the SAM and promotes differentiation • Acts via at least 4 different receptor protein kinases • CLV1 best understood: sets off cascade that results in repression of WUS

30. Other Peptides • Clavata 3 type • Large gene family ~ 150 members • Act over short distances • Promote differentiation

31. Other Peptides • Clavata 3 type • Large gene family ~ 150 members • Act over short distances • Promote differentiation

32. Other Peptides • Clavata 3 type • Large gene family ~ 150 members • Act over short distances • Promote differentiation • Act via Pm-bound receptor protein kinases

33. Carbohydrates • Cell wall fragments mainly involved in stress signaling

34. Carbohydrates • Cell wall fragments mainly involved in stress signaling • Released by pathogens digesting cell walls

35. Carbohydrates • Cell wall fragments mainly involved in stress signaling • Released by pathogens digesting cell walls • Can also inhibit cell growth • Role in normal development is uncertain