Effect of Strigolactones in plant signal transduction and development

Rakesh sarma Ph.D Research scholarDepartment of Plant Physiology BHU,Varanasi

Introduction

Striga spp growing on rice (a) Striga hermonthica, (b) Striga asiatica

Member of Orbanchaceae family.Parasitize cereal crops rice, sorghum and maize.Hemiparasites - green leaves -unable to perform sufficient photosynthesis for their survival. elevated transpiration rates enabling them to obtain larger quantities of water and nutrients from their host.

(a) Orobanche Cumana growing on sunflower, (b) Orobanche aegyptiaca growing on tomato. Holoparasites that lack chlorophylls. They parasitize dicotyledonous crops including tomato, tobacco,carrot, clovers, cucumber, sunflower, and legumes.

Life cycle of a root parasitic plant, Orobanche minor. (a) Seed germination is elicited by host-derived stimulants, including strigolactones. (b) Seedling attaches to host root with haustoria. (c–d) Parasite tubercles grow underground for several weeks or months before emergence of the flowering shoots. (e) The parasite produces a large number of seeds, which remain viable for many years in soil.

History Discovery: 1960 (germination stimulant ) Name: root parasitic plant strigaShinjiro Yamaguchi (2008): inhibits shoot

branching.Recently, role in plant development and

adaptive responses.

Biosynthesis and Perception

of SLs

A model of SL signalling pathway through SL hydrolysis

Germain et al., 2013

5-Deoxystrigol, strigol and orobanchol are natural SLs. GR24 is a synthetic SL analog.

MutantRMS (Ramosus of Pea)DAD(Decreased apical dominance of Petunia)MAX (More axillary growth of Arabidopsis)D (Dwarf) or HTD (high tillering dwarf) of

Rice

Pea wild-type plant (left) and rms1 high branching mutant plant (right)

Arabidopsis strigolactone-deficient mutant max3 of shows exuberant branching

b | A schematic representation of grafting experiments carried out with Arabidopsis thaliana mutants that are impaired in the strigolactone pathway. These mutants were identified on the basis of their increased branching phenotype. The increase in branching observed in the strigolactone biosynthesis mutants (more axillary growth 1 (max1), max3 or max4) can be restored to the wild-type levels by grafting the mutant shoots onto wild-type roots, demonstrating that the inhibitor can move from the roots to the shoots.

Domagalska and Leyser (2011)

Spira et al., 2012

Role of SLs in Plant

Development

Seed GerminationNatural and synthetic SLs have moderate to

potent germination activity.Hydroxy-SLs are 10-fold to 100-fold more

active than their acetates and other conjugates.Germination stimulation activity of SLs on one

parasitic plant species may be different from that on the other species. For example, under laboratory conditions, sorgomol, originally isolated from sorghum root exudates, is more active on Striga spp. than on Orobanche spp.

Secondary Growth Agusti et al. (2011): Pea and Eucalyptus plants

Leaf SenescenceDelayed

leaf senescence mutant

Cheng et al., 2013

Abbreviations: P, primordium; DM, distal meristem; PM, proximal meristem; AM, apical meristem; BM, basal meristem; TZ, transition zone; EZ, elongation zone; DZ, differentiation zone; FC, founder cell .

Role of Strigolactones

in Nutrient-Stress

Marzec et al., 2013

Czarnecki et al., 2013

Effect of SL treatment on survival of SL-deficient and SL-response mutants and WT plants. (A) Three-wk-old WT and SL-deficient max3-11 and max4-7 and SL-signaling max2-3 mutant plants before drought stress. (B) Three-wk-old plants subjected to a drought stress ( 5 mL of 5 μM SL or water, the first day and from the 7th to the 13th days and twice in a day at 10:00 AM and 4:00 PM). Plants were photographed 3 d subsequent to rewatering and after removal of inflorescences from the surviving plants. (C) Nonstressed WT and max plants sprayed with 5 mL of 5 μM SL or water as shown in B. (D) Percent survival of mutant and WT plants sprayed with SL or water and subjected to a drought stress.

Ha et al., 2013.

ConclusionStrigolactones are signaling compounds made by plants. They have

two main functions: 1. Endogenous hormones to control plant development. 2. Components of root exudates to promote symbiotic interactions

between plants and soil microbes. Some plants that are parasitic on other plants have established a

third function, which is to stimulate germination of their seeds when in close proximity to the roots of a suitable host plant.

SL acts as positive regulator of plant responses to drought and salt stress, which was associated with shoot- rather than root-related traits.

Genetic variation in strigolactone responses could provide an opportunity to breed plants with superior nutrient use efficiency and ability to form symbiotic associations.

We have a long history of research in We have a long history of research in plant hormones, we are still ignorant plant hormones, we are still ignorant about many things. I think there are about many things. I think there are

other plant hormones that still remain other plant hormones that still remain undiscovered, and I really hope to find undiscovered, and I really hope to find

them.” them.”

Shinjiro YamaguchiShinjiro Yamaguchi

Future perspective

THANK YOU for attention