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Growth regulators Auxins Cytokinins Gibberellins Abscisic Acid Ethylene Brassinoteroids

Growth regulators Auxins Cytokinins Gibberellins Abscisic Acid Ethylene Brassinoteroids Jasmonic Acid Salicylic Acid Strigolactones Nitric Oxide Sugars. Brassinosteroids First identified in pollen from Brassicas (= brassins) Stimulate both elongation and cell division

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Growth regulators Auxins Cytokinins Gibberellins Abscisic Acid Ethylene Brassinoteroids

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  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

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