Strigolactones (New plant hormone in action) The sessile life style of plants largely depends on endogenous metabolites to finetune their growth and development against changing environmental conditions Sessile life style of plants Generally, plant hormones (phytohormones) attributes adaptability to the ever-changing environmental conditions and to various biotic-abiotic constrains. Mostly, different phytohormones have functional distinctions. In general, auxin, cytokinins (CK), gibberellins (GA), brassinosteroids (BR) and ethylene predominantly have their role in plant growth and developmental events, Phytohormones Abscisic acid (ABA) and jasmonic acid (JA) act as the abiotic and biotic stress response molecules The recent addition to the class of plant hormones are strigolactones (SLs) Considering the complexity of plant life, the existence more signalling molecules are anticipated and experimental biology occasionally comes up with new signalling molecules in plants. New plant hormones 2008, Nature 455: 195-202 2008, Nature 455: 189-194 Strigolactones are initially identified as a seed germination stimulants of parasitic plants; Striga The most challenging biotic constrain in cereal production especially in African region is parasitic plants of Striga species. Approximately 25 million people in Africa alone are affected by Striga and causing losses estimated to 1 billion USD per year. Initially identified function Cook et al., 1972 Why Striga infestation is hard to control? • After attachment to the host root, Striga seedlings grow underground and emerge already after causing severe damage to the host plant. • Each Striga plant can produce up to 20,000-50,000 seeds. • These seeds are dust like, can be easily dispersed by wind, water, contaminated crop seeds, and by people. • They can survive over 15 years in dormancy stage until come in contact with germination stimulant. Severity of Sriga infestation of maize fields Promoting hyphal branching of symbiotic arbuscular mycorrhiza (AM) fungi Facilitates beneficial symbiotic interaction with the host plant Akiyama et al., 2005 AM fungi penetration (red) through plant root epidermal cell Host plant and AM fungi interaction AM Fungi maintains a symbiotic relationship with host plant AM Fungi absorbs nutrients such as nitrogen and phosphorus from soil and supplies to the plant. The plant gives ten to twenty percent of the carbon they generated through photosynthesis to the fungus Host plant and AM fungi relationship Orobanche crenataGlomus intraradices Arabidopsis Pea Rice Petunia 2008, Nature 455: 189-194 MAX- MORE AXILLARY GROWTH RMS-RAMOUS D-DWARF DAD-DECREASED APICAL DOMINANCE Strigolactone quantification Measurement of orobanchyl acetate (grey) and the second strigolactone (black) in different genotypes 2008, Nature 455: 189-194 Nature 455: 189-194 Role of Strigolactone in plant development Al-Babili and Bouwmeester, Annu. Rev. Plant Biol. 2015 + Biotic and abiotic stress responses GR24 Lateral root development Adventitious root development Axillary bud out growth Stem secondary growth Internode length Leaf senescence Root hair development Role of Strigolactone in drought stress Ha et al., 2013 Strigolactone biosynthesis 9-cis/all-trans isomerization (DWARF 27-isomerase) Carotenoid cleavage dioxygenases 7 (CCD7) Carotenoid cleavage dioxygenases 8 (CCD8) Carlactone oxidase (CO) Orobanchol synthase (OS) Strigolactone signalling Unique step in plant signalling Serine Histidine Aspartate GR24 Strigolactone transport ABC protein PLEIOTROPIC DRUG RESISTANCE 1 (PaPDR1) is apically localized in root tip cortex cells and outer-laterally localized in the root hypodermis. PaPDR1 plays a key role in regulating shootward and outward directional strigolactone transport. Sasse et al., 2015 C E cook et al.,1966 Akiyama, et al., 2005 Strigol Al-Babili and Bowmeester , 2015Think of possible applications Possible applications of SL research Regulates agronomically important traits Better uptake of soil nutrients Solution for Striga infestation Solution for Striga infestation Most commonly used control methods are hand weeding, crop rotation, improving soil fertility, use of tolerant cultivars and inventing ‘suicide’ germination compounds. Inventing ‘suicide’ germination compounds Toh et al., 2015 Offers opportunity to design and synthesize Striga specific SL antagonists and agonists. Receptor-ligand binding affinity Importance of strigolactone research • Possible direct application in agriculture. • Diverse role in plant development. • Genetic tools generated and research going on different plant species in parallel. • Very unique signalling mechanism. Genome Wide Association Study (GWAS) GWAS is an alternative to traditional QTL mapping GWASs typically focus on associations between single-nucleotide polymorphisms (SNPs) and traits like major human diseases These are positions in genome where some individuals have one nucleotide and others have different. Around 325 million SNPs have been identified in the human genome,15 million of which are present at frequencies of 1% or higher across different populations worldwide. The basic principle of GWAS is to correlate genetic variation with physical characteristics. Wide range of human diseases such as sickle-cell anemia, Osteoporosis, atherosclerosis, β-thalassemia and cystic fibrosis result from SNPs. Microarray-based genome-wide association studies (GWAS) have been the most common approach for identifying disease associations across the whole genome GWAS Identifying candidate genes of Strigolactone pathways using Genome Wide Association Study • unique collection • 242 ecotypes - 28 countries Arabidopsis thaliana Col0 ctrl Col0 GR24 Genome Wide Association Study (GWAS) Various root traits were analyzed as readouts in 242 accessions Dr. Wolfgang Busch Total length, Euclidian length, Root tortuosity, Root growth rate, Relative root growth, Root angle, Root direction index, Root horizontal index, Root vertical index, Root linearity, Lateral root number Root width in different height of the root Pilot experiment Concentration of GR24 100 nM Methodology gas sterilization stratification (72 hod, 4ºC) making media Control/Strigolactone (GR24 100 nM, DMSO) plating seeds (23 ecotypes + 1 Col- 0) growing in culture room, 3 days (21ºC, 16/8) scanning 1-5, 8, 11, 15, 18 day data processing Methodology Images 1200 dpi FIJI Software for images analysing BRAT Busch Lab Analysis Toolchain GWAS Genome wide association mapping Selection of candidate genes Follow up experiments Manhattan plot depicting several strongly associated risk loci Control Is-1 GR24 Is-1 GWAS parameters 10 accessions from each extremes will be selected for running GWAS Control KAR-1 GR24 KAR-1 Lateral root number day 8 day 11 day 5 Genes - Protein of unknown function (DUF506) Preliminary Outcomes KAR 1 GWAS results GWAS results http://signal.salk.edu/atg1001/3.0/gebrowser.php Advantages and disadvantages of GWAS over QTL mapping Advantages • Higher mapping resolution • Reduced research time (no creation of bi- or multi-parental populations) • Larger number of detectable alleles Disadvantages • Low statistical power than QTL mapping can lead to false positive • Hard to detect rare alleles • Necessity of large sample volume