Hormones: Gibberellic acids (GA) Bakanae: crazy seedling (rice) Gibberella fujikuroi (GA 3 ) rare in plants Increased plant height Reduced seed set and yield

Gibberellic acids (GA) structures

Hormones: Gibberellic acids (GA) Plant height regulators ……and more Gregor and his peas….. (1866) GA 1 is relevant for cell elongation GA 20 regulates germination

Gibberellic acids: effects on plants Growth of inflorescence: elongation of internodes Seed germination: induction of  -amylase Breaking dormancy

Gibberellic acids: effects on plants Degradation of GA 1 through GA 2-oxidase 35SGA 2-oxidase

Gibberellic acids: effects on plants GA 1 inhibitor AMO reverses GA effect GA 1 stimulates elongation in spinach

GA effects on plants Fruit growth and ripening

GA effects on plants Tuber formation Short days: less GA 1 Long days: more GA 1

Auxin Gibberellins Auxin promotes GA biosynthesis (Synergy of phytohormones)

How does GA work? Represses genes needed for growth GA signal migrates into the nucleus and inactivates repressors RGA/GAI

GA signaling intermediate Signaling protein

Hormones Communication among cells, tissues and organs Cytokinin: What is it? Where and how is it made? What effect is due to cytokinin? How does it work?

Cytokinin and tissue culture Crop breeding and tissue culture selection

Together with auxin regeneration of callus tissue IAA (mg/l) Kinetin (mg/l)

Cytokinin effects: Cytokinin biosynthesis in the root also: young tissues, embryos, meristems Transport through xylem to shoot and leaves catabolized through cytokinin oxidase Isopentenyl-adenine (basic cytokinine structure)

Cytokinin effects: senescence Green island formation on fall leaves Delay and reversal of senescence

Overproduction of cytokinin biosynthesis genes: delayed senescence

Cytokinin effects: pathogens Witches broom: leafy galls on trees Rhodococcus fascians Agrobacterium tumefasciens: crown gall

Identifying a receptor: cre1 wild-type cre1

Identifying a receptor family: ahk2, ahk3, cre1

Cytokinin signal is transduced to its response genes in the nucleus Cytokinin signal Cytoplasm

Signal transduction of cytokinin goes through protein kinases

Signal transduction through two- component signal transducers

Ethylene: it’s a gas!! CC H H H H Biologically active at less than 0.1ppm Transported as ACC Synthesized in ripening fruit and senescing tissues Induced by auxin, draught, wounding, cold, stress, fruit ripening, senescence, pathogen attack

Ethylene: it’s a gas!! Biologically active at less than 0.1ppm Transported as ACC Synthesized in ripening fruit and senescing tissues Induced by auxin, draught, wounding, cold, stress, fruit ripening, senescence, pathogen attack 1864 illuminating gas powered street lights defoliate trees 1901 Neljubov identifies ethylene as phytohormone 1917 Doubt identifies ethylene as defoliant 1934 ethylene biosynthesis in plants detected 1935 ethylene is the “ripening hormone”

Auxin prevents abscission However: unphysiological auxin concentrations have herbicide effects (agent orange)

Antisense-Inhibition of ACC-Oxidase stops flower senescence

Ethylene the defoliant…. …and fruit ripening hormone

Ethylene: triple response Triple response: - thickening of hypocotyl, radial growth - eduction of cell elongation in hypocotyl and root - exaggerated curvature of apical hook, reduced geotropism

Understanding the hormone: Searching for ethylene mutants etr1 ctr1 Ethylene resistant Constitutive triple response Air Ethylene

Understanding the hormone: Searching for ethylene mutants (ETO1) Air Ethylene eto1 Ethylene overproducer Wild-type - Ethylene overproducer show same phenotype as ctr1 - ctr1 not reversible by inhibitors of ethylene biosynthesis - eto phenotype is reversed by ethylene synthesis inhibitors ETO1 has de-regulated ethylene biosynthesis

Understanding the hormone: Searching for ethylene mutants (ETR1) Ethylene resistant AirEthylene AirEthylene Wild-typeEtr1 etr1 Etr (ethylene resistant) Ein (ethylene insensitive) Ethylene receptors

Understanding the hormone: Searching for ethylene mutants (CTR1) ctr1 Constitutive triple response air Wild-type ctr1 airethylene Recessive loss-of-function ctr1 mutations: - Constitutive activation of ethylene response - Ethylene induced genes are always “on” - Constitutive triple response CTR1 leads to inhibition of ethylene response in absense of ethylene

Genetic epistasis Phenotype of first gene is masked by phenotype of a second gene ETR1, EIN4, ETR2 EIN2, EIN3, EIN5 CTR1 etr1-3 ctr1-1 ein4-1 ctr1-1 etr2-1 ctr1-1 ein2-1 ctr1-1 ein3-1 ctr1-1 ein5-1 ctr1-1 constitutive triple response ethylene insensitive