WELCOME

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Molecular Basis of Aerial Plant Part Architecture in Rice

Presented By VANISHRI, B.R.

PALB 4249

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CONTENTS

Introduction Tillering Panicle morphologyPlant heightCase studyConclusion

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Plant Architecture Plant architecture is referred to as the three

dimensional organization of the plant.

Crop plants with desirable architecture are able to produce much higher grain yields.

In case of the “Green Revolution” in which grain yields have been significantly increased by growing lodging-resistant semi- dwarf varieties of wheat and rice.

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RICE PLANT

Rice is an annual grass with round, hollow and jointed stems (culms) that bear panicles.

Generally, rice plant growth is divided into three stages:

1. Vegetative stage2. Reproductive3. Grain filling stage

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Rice plant architecture• Rice is an ideal system for studying plant architecture

of cereal crops.

• Rice plant architecture, a collection of the important agronomic traits that determine its grain production, is mainly affected by factors including

1. Tillering 2. Plant Height 3. Panicle Morphology

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Tillering

Rice tillering occurs in a two-stage process: the formation of an axillary bud at each leaf axil and its subsequent outgrowth.

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Genes Controlling Tillering

• MONOCULM 1 (MOC1)• LAX PANICLE (LAX 1)

Genes involved in strigolactone biosynthesis and signalling

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Wang and Li, 2011

Genes Involved In Tillering

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• Neither the extremely spreading nor the compact plant type is beneficial to rice grain production.

Genes involved in regulating the tiller angle in rice:• LAZY1 (LA1) • TAC1 (Tiller Angle Control 1)• PROG1 (PROSTRATE GROWTH1 )

Tiller Angle

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LAZY1 (LA1)

Negative regulator in polar auxin transport (PAT).

Mutations of LA1 enhance PAT greatly and alter the endogenous IAA distribution in shoots, leading to the tiller-spreading phenotype of rice plants.

It regulates the lateral organ angle and mediates branching and leaf formation (Li et al., 2007).

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TAC1 (Tiller Angle Control 1)• TAC1, positive regulator of rice tiller angle.

Mutation in TAC1 • Sharp upward asymmetrical growth of the base of

the culm.• Compact plant architecture with erect tillers (Yu et

al., 2007).

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PROSTRATE GROWTH1 (PROG1)

• Prostrate growth habit to erect tiller growth of rice.

• Transcription factor.

• Expression site: unelongated basal internodes of the culm.

• Mutation in PROG1 leads to a phenotype of significantly less vertical tiller angle.

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• Tiller has the potential to produce a panicle by transitioning from a vegetative SAM(shoot apical meristem) into a reproductive SAM.

• Tillers that produce panicles are termed effective tillers, and they contribute to the grain yield.

Panicle Morphology

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• Rice panicle develops into three types of axillary meristems,

Rachis-branch Meristems, Lateral Spikelet Meristems Terminal Spikelet Meristems.

• The initiation and outgrowth of these meristems determines rice panicle morphology.

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Major Steps In The Rice Panicle Development

(A) Formation of the first bract primordium indicating the transition from the vegetative phase to reproductive phase;

(B) Formation of the primordia of the primary branches(PB) from the base of bracts;

(C) Formation of the primordia of the secondary branches(SB) from the base of each PB primordium;

(D) Formation of the terminal and lateral spikelet meristem primordia on the rachis-branches (primary and/or secondary branches) and differentiation of the spikelet primordia

Wang and Li,2005

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Key Genes Controlling Rice Panicle Architecture

Wang and Li, 2008

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Models representing the function of FZP during the development of rice spikelets

Komatso et al., 2003

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Plant Height

Rice stem elongation starts at the beginning of panicle initiation and is mainly ascribed to the rapid elongation of cells in the top 4–6 internodes.

Gibberellins(GA) and Brassinosteroids(BR) have been revealed to play major roles in modulating rice plant height.

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Wang and Li,2008

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CASE STUDY

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INTRODUCTIONPlant architecture, a complex of the important

agronomic traits that determine grain yield, is a primary target of artificial selection of rice domestication and improvement.

Genetic identification and functional analysis of the PLANT ARCHITECTURE AND YIELD 1 (PAY1) gene in rice.

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MATERIALS AND METHODS

Plant materials :• YIL55 (a wild rice introgression line )• The PAY1 mutant

YIL55 mutagenized with EMS to generate a library for genetic screening of mutants with altered plant architecture.

They identified a mutant with greatly changed plant architecture, referred to as PLANT ARCHITECTURE AND YIELD 1 (PAY1).

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Phenotype of wild-type (YIL55) and PAY1 mutant.

(a) Introgression line YIL55 and the PAY1 mutant at maturity stage.(b) Main panicle of YIL55 and PAY1 mutant.(c) Stem structure of YIL55 and PAY1 mutant. (d) Cross-sections of the fifth internode(e) The diameter of the fifth internode between YIL55 and PAY1 mutant. (f) Comparison of plant height, number of panicles per plant, grain number per

panicle and grain yield per plant between YIL55 and PAY1 mutant plants.

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Cloning and Characterization of PAY1

• The F1 plants from the cross between PAY1 and YIL55 showed a similar phenotype to the PAY1 mutant .

• F2 plants, showed a segregation rate of the PAY1 mutant and YIL55 plants fitting a 3:1 ratio.

• These results indicated that the PAY1 mutant phenotype was controlled by a single dominant gene.

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CLONING

• F2 populations were generated from the cross between the PAY1 mutant and Nipponbare

• PAY1 mapped between the single sequence repeat markers RM339 and RM223 on the long arm of chromosome 8.

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Molecular identification of PAY1

(a) PAY1 was mapped in the interval of RM339 and RM223 on the long arm of chromosome 8.

(b) PAY1 was delimited to a 51-kb region between the sp5 and sp7 markers.(c) Annotation of the 51-kb region harboring PAY1 on Nipponbare BAC AP004691.(d) PAY1 structure and the mutation site in PAY1 mutant

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Genetic Confirmation

• To verify altered plant architecture caused by the single nucleotide change in the LOC_ Os08g31470 gene.

• They generated transgenic YIL55 plants with overexpression of cDNA of the PAY1 mutant

• Real-time quantitative PCR (RT- qPCR) analysis showed that the expression levels of PAY1 were much higher in transgenic than in control plants.

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Experimental Procedure• The entire coding sequence of PAY1 cDNA , a 1773-bp

fragment, was inserted into the vector pCAMBIA1301 driven by the maize Ubiquitin promoter to form the over expression construct pOE.

• The construct was introduced to Agrobacterium tumefaciens strain EHA105 and subsequently transferred into YIL55.

• There were 18 independent transgenic lines harvested, and two lines (pOE6 and pOE8) were used for phenotypic evaluation.

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Comparison of control plant (CL3) and PAY1-overexpression transgenic plants .

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The PAY1 mutant shows reduced polar auxin transport(PAT) activity

PAT plays a key role in the regulation of many aspects of plant growth and development.

The basipetal and acropetal indole-3-acetic acid (IAA) transport in etiolated coleoptiles of wild-type and PAY1 plants were compared.

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3 groups of 5 days old Coleoptile Segments of 2cm length

incubation

Liq. Half strenght MS media, 100 rpm for 2hr

One end of apical/basal end is submerged in Half strenght MS media

To remove endogenous IAA

0.35% phytagel500nm [3H]IAA

DarkRT2hr

NPA (N-1-naphthylphtalamic acid) applied to media for one group

Submerged end is washed with Half strenght MS media, 3times

Radioactivity of each section was counted by Liquid scintillation counter.

20 hr incubation in scintillation liquid

PAT Assay

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Results and Discussion

Comparision of PAT between YIL55 and PAY1 mutant in dark grown coleoptiles

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Comparision of auxin content in the tip of dark grown coleoptiles between YIL55 and PAY1 mutants

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PAY1 Used For High-yield Breeding

To evaluate the PAY1 potential application for optimizing rice plant architecture and increasing grain yields

They introduced the PAY1 into Teqing (TQ)

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• The NILs were generated using continuous backcrossing between PAY1, as the donor, and elite indica variety Teqing as the recurrent parent.

• BC3F3 generation plants were used for phenotype analysis.

Continued

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Phenotype of TQ and TQ-PAY1 NIL Plants

(a) Gross morphologies of TQ and TQ-PAY1-NIL plants at the maturity stage.(b) Stem structure of TQ (left) and TQ-PAY1-NIL (right) plants. (c) Comparison of the main panicle between TQ and TQ-PAY1-NIL plants. (d) Cross-sections of the fifth internode between TQ and TQ-PAY1-NIL plants.

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CContd…….

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• The PAY1 mutant showed characteristics of ideal plant

architecture compared with the wild-type YIL55 via affecting PAT activity and altering endogenous indole-3-acetic acid distribution.

• The NILs with Teqing genetic background demonstrated that PAY1 could shape better plant architecture and enhance grain yield of rice.

• PAY1 is an important dominant regulator of rice plant architecture and would be useful for rice genetic improvement and breeding of new varieties with increased grain yield, thus contributing to global food security.

CONCLUSION

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SUMMARYRice is one of the most important staples and feeds more than half of the world’s population.

The ability to produce more food in the same acreage is crucial to feeding an increasing world population, and therefore rice attracts tremendous attention in crop improvement.

Elucidation of the molecular mechanisms underlying rice plant architecture will provide a solid basis for modifying the plant and in turn help to increase the yield.

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