Lecture 5 Plant hormones and Signal transduction PLSC 452/552 1/23/14 Department of Plant Sciences Neal Stewart Lab

Brain teaser Little Johnny nails a sign 90 cm off the ground to a tree outside of his clubhouse that says “no girls allowed.” If the tree grows 12 cm every year, at what height will the sign be when Little Johnny returns as Big Johnny in 15 years?

Overview Define “hormone” as a functional compound. What is the function and importance of hormones? Know the major plant hormones Understand real-world application of hormones Importance of hormones for tissue culture: introduction

What is a hormone? Biochemical which regulates growth based on biological and environmental influences Synonyms: Plant hormones, plant growth regulators (PGRs), phytohormones Regulate growth and development Mobile throughout plant Environment and stress responsive

Major plant hormones Auxin – Greek: auxein; to grow or increase Cytokinin – cytokinesis (cell division) Abscisic acid – abscission Jasmonic acid – found in jasmine oil Gibberellic acid – pathogen Gibberella Ethylene – chemical brother to ethanol Brassinosteroids – derived from Brassica spp.

Finding plant hormones Observational: Darwin stumbles on auxin Noticed grass tips grow toward light With tip growth responded to light Without tip growth had no response Mutation screening: (aka forward genetics) Dwarf plants are can be hormone deficient

ABRC teaching tools website

General hormone biochemistry Present in all cells at various levels Classes of hormones work in signal cascades Hormone-receptor interactions Respond to a host of factors and biological needs Abiotic Water stress Light Nutrient deficiency Biotic Growth Development Herbivore stress

Hormone biosynthesis Made from four biosynthetic pathways: Terpenoids AMP + IPP (cytokinins) Carotenoid breakdown (abscisic acid) Diterpene (gibberellic acid) Triterpene (brassinosteroids) Fatty acids (jasmonic acid) Tryptophan (auxins) Methionine (ethylene)

KEGG database: http://www.genome.jp/kegg/

Auxins Greek: auxein; to grow or increase Apical dominance growth Cell elongation Hormone level very important 2, 4-dichlorophenoxyacetic Acid http://pubchem.ncbi.nlm.nih.gov/

http://www.nsf.gov/news/news_images.jsp?cntn_id=104205

Taiz and Zeiger. 2002. Plant Physiology, 3rd Ed.

Auxin: Apical dominance http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/Auxin.html

Cytokinin Cytokinesis (cell division) Accidently added degraded DNA to medium Organization and development of xylem tissue Response to light Lateral growth of shoots Open stomata Kinetin http://pubchem.ncbi.nlm.nih.gov/

Application: cotton spraying Adding cytokinins to young cotton increase drought-resistance Arizona – 31% US cotton, highest yield acre-1

Auxin and cytokinin ratio importance Auxin alone = Large cells (no division) Cytokinin alone = Cells have no change Auxin + Cytokinin = Normal cell growth and division Auxin + >Cytokinin = Shoot growth >Auxin = Cytokinin = Root growth

Auxin Cytokinin http://users.ugent.be/~pdebergh/pri/pri4ez04.jpg

Abscisic acid (ABA) Originally implicated in leaf and fruit abscission Involved in leaf senescence Maintains seed dormancy (opposed to GA) Involved in stomata regulation (closes) Single hormone unit http://pubchem.ncbi.nlm.nih.gov/

http://www.rikenresearch.riken.jp/eng/research/6121

Jasmonic acid First identified in jasmine oil Response to biotic stress Wounding induces JA biosynthesis Microbial and fungal invasion Plant growth effects similar to auxin Specialty growth structures http://pubchem.ncbi.nlm.nih.gov/

Jasmonic acid: Plant-insect co-evolution Tri-trophic interactions Degenhardt (2009) Plant Physiology 149:96-102

Jasmonic acid: Pathogen response http://park.itc.u-tokyo.ac.jp/biotec-res-ctr/kampo/eng/research_plant.html

Gibberellic acid Originally found in Gibberella (rice pathogen) Responsible for ‘foolish seedling’ phenomenon Uninhibited growth until breaking Involved in cell elongation Flowering and seed germination http://pubchem.ncbi.nlm.nih.gov/

Modification of GA in rice Miyako Ueguchi-Tanaka 2005 Nature 437, 693-698

Spraying GA for increased fruit yield GA induces fruiting in absence of seed http://www.extension.org/pages/31607/using-plant-growth-regulators-to-increase-the-size-of-table-grape-berries#.Ut9EYbROmM8

Ethylene: the cell phone of PGRs A hydrocarbon gas Involved in fruit ripening, stress response Inhibition of growth in dark conditions Excess ethylene inhibits callus growth

Conversational Plants? Ethylene production increases during stress Drought Heat Perceived by neighboring plants Unstressed plants induce stress pathways

Brassinosteroids Stress responses Stem elongation Seed germination Switchgrass suspension cells have minor amounts of lignin (small amounts of H monolignols) Addition of brassinolide induces normal lignin formation and composition Stem elongation Seed germination Pollen tube growth Cell differentiation control Brassinolide http://pubchem.ncbi.nlm.nih.gov/

Overview of hormone mutants Cytokinin mutant Brassinosteroid mutant Cytokinin mutant closer look Phenotypes associated with the brassinosteroid, ethylene, cytokinin and abscisic acid receptor mutants. All images are shown against wild type for comparison. (A) The brassinosteroid receptor mutant bri1-301 (bottom) shows a dwarf phenotype. (B) The dark-grown ethylene receptor mutant ein4 (right) lacks the triple response (left; see main text). (C) The triple cytokinin receptor mutant cre1 ahk2 ahk3 (right) shows reduced growth. (D) The root vascular bundle normally consists of xylem, phloem and procambium cell files, whereas in wol (bottom), or in cre1 ahk2 ahk3 (not shown), there are fewer vascular cell lineages, all of which differentiate as protoxylem. The vascular bundle is encircled by a layer of pericycle cells (asterisks) (E) The abscisic acid receptor mutant fca (right) flowers later than wild type, as demonstrated by increased leaf number at flowering. Scale bars: in C, 2 mm; in D, 10 μm. [A is reprinted, with permission, from Cano-Delgado et al. (Cano-Delgado et al., 2004); B is reprinted, with permission, from Hua et al. (Hua et al., 1998); E is reprinted, with permission, from Amasino (Amasino, 2003).] Ethylene mutant grown in dark Abscisic acid mutant Bishopp A et al. Development 2006;133:1857-1869

Hormones (PGR) pathways PGRs work in complex cascades to produce signals Synergistic Anatognistic Variety of actions in cell Gene transcription Protein degradation http://chriscarterart.wordpress.com/2010/05/09/mothers-day-2/mikado-plant-watercolor-sketch-chris-carter-050910/

Arabidopsis histidine kinase sensing and signaling; 2) A histidine phosphotransferase protein nuclear translocation; 3) A response regulation transcription activation; and 4) a negative feedback loop through cytokinin-inducible ARR gene products. http://molbio.mgh.harvard.edu/sheenweb/cytokinin_signaling.html

Introduction: the importance of manipulation of hormones for tissue culture Auxins and cytokinins are very important Higher auxin induces root growth Equal ratio induces callus and cell enlargement Lower auxin induces shoot growth Gibberellic acid germinates difficult seeds Add brassinosteroids for cell wall induction

Lecture summary Hormones are biochemicals that regulate plant growth based on biological and environmental cues Auxin and cytokinin are key for plant growth Abiotic and biotic stress response is regulated by hormones Cell signaling is regulated by specific receptors on cell membranes