Growth regulators 1 Auxins 2 Cytokinins 3 Gibberellins

Growth regulators 1. Auxins 2. Cytokinins 3. Gibberellins 4. Abscisic Acid 5. Ethylene 6. Brassinoteroids 7. Jasmonic Acid 8. Salicylic Acid 9. Strigolactones 10. Nitric Oxide 11. Sugars

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

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

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

• 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

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

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 E 3 ligase

Strigolactones Growth regulators derived from carotenoids • Trigger degradation of proteins that stimulate branching by an E 3 ligase • Trigger degradation of SMAX 1 via MAX 2 E 3 receptor • Allows seed germination, seedling growth & development • Link with karrikin signaling

Karrikins Growth regulators derived from carbohydrates by burning • Stimulate germination of dormant seeds waiting for fire • Trigger degradation of SMAX 1 via MAX 2 E 3 receptor • Allows seed germination, seedling growth & development

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

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 NPR 1

Salicylic Acid SA induces expression of defense proteins via NPR 1 • Ethylene and Jasmonic Acid induce an overlapping set of defenses

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

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

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

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

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

Peptides 1. Systemins • 18 aa peptides released in response to herbivory

Peptides 1. Systemins • 18 aa peptides released in response to herbivory • Trigger synthesis of jasmonic acid & ethylene in target cells

Peptides 1. Systemins • 18 aa peptides released in response to herbivory • Triggers synthesis of jasmonic acid & ethylene in target cells • Some attract parasitoids

Peptides 1. Systemins • 18 aa peptides released in response to herbivory • Trigger synthesis of jasmonic acid & ethylene in target cells • Activate defense genes

Peptides 1. Systemin • 18 aa peptide released in response to herbivory • Triggers synthesis of jasmonic acid & ethylene in target cells • Activates defense genes 2. hydroxyproline-rich glycopeptides • Unrelated structures, but similar size and also activate JA

Other Peptides 1. Clavata 3 -Wuschel signaling • WUSCHEL is a transcription factor made in the “Organizing Center” of the shoot apical meristem • Promotes stem cell formation

Other Peptides 1. 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

• 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

• 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

• 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 • CLV 1 best understood: sets off cascade that results in repression of WUS

Other Peptides 1. Clavata 3 type • Large gene family ~ 150 members • Act over short distances • Promote differentiation

Other Peptides 1. Clavata 3 type • Large gene family ~ 150 members • Act over short distances • Promote differentiation • Act via Pm-bound receptor protein kinases

Carbohydrates Cell wall fragments mainly involved in stress signaling

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

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