Introduction to Plant DevelopmentIntroduction to Plant Development

BIO 274BIO 274--0101Plant MorphologyPlant Morphology

Fall 2007Fall 2007Discussion 2Discussion 2

Plant Morphology Plant Morphology –– study of the morphology (physical form study of the morphology (physical form and external structures) of plantsand external structures) of plants

Plant morphology examines the pattern of development, the Plant morphology examines the pattern of development, the process by which structures originate and mature as a plant process by which structures originate and mature as a plant growsgrows

Plant Anatomy Plant Anatomy –– study of the internal structure of plants, study of the internal structure of plants, examines plant at cellular levelexamines plant at cellular level

Plant Physiology Plant Physiology –– study of the function of physiology study of the function of physiology (mechanical, physical and biochemical functions of living (mechanical, physical and biochemical functions of living organisms ) of plantsorganisms ) of plants

Plant Development Plant Development –– studies the formation of the embryo from studies the formation of the embryo from a zygote, seed germination, development of mature vegetative a zygote, seed germination, development of mature vegetative plant from the embryo, the formation of flowers, fruits and plant from the embryo, the formation of flowers, fruits and seeds and environmental factors that affect these growth seeds and environmental factors that affect these growth processes.processes.

Molecular genetics and the use of molecular biology Molecular genetics and the use of molecular biology tools has greatly improved our understanding of plant tools has greatly improved our understanding of plant development.development.

Plant morphologist, anatomist, and physiologist all Plant morphologist, anatomist, and physiologist all use molecular genetics to investigate various aspects use molecular genetics to investigate various aspects of plant development.of plant development.

Why is genetics so important in understanding plant Why is genetics so important in understanding plant development?development?

Genetics helps researchers identify genes that control Genetics helps researchers identify genes that control plant development.plant development.

Many of the scientist that study plant development use a Many of the scientist that study plant development use a ““toolboxtoolbox”” of of mutants that affect a developmental processmutants that affect a developmental process

These mutations are recognized by their phenotype; abnormalitiesThese mutations are recognized by their phenotype; abnormalities in in developmentdevelopment

Phenotype Phenotype –– physical appearance of an organism; description of its physical appearance of an organism; description of its traitstraits

Genotype Genotype –– genetic makegenetic make--up of an organismup of an organism

Characterization of genetic mutants is often used to connect theCharacterization of genetic mutants is often used to connect these aberrant se aberrant phenotypes to the genes responsible for that developmental procephenotypes to the genes responsible for that developmental processss

Many of these genes will be discussed this semester so it is impMany of these genes will be discussed this semester so it is important that ortant that you understand the basic principles of gene expressionyou understand the basic principles of gene expression

Genetic ScreensGenetic ScreensPlants carrying various mutations will often have an abnormal Plants carrying various mutations will often have an abnormal phenotype when compared to wildphenotype when compared to wild--type plantstype plants

–– WildWild--type type –– the typical form of an organism, strain, gene or the typical form of an organism, strain, gene or characteristic as it occurs in naturecharacteristic as it occurs in nature

–– Mutant Mutant –– an individual, organism, or genetic character an individual, organism, or genetic character arising from an instance of mutationarising from an instance of mutation

–– Mutation Mutation –– changes to the base pair sequence of genetic changes to the base pair sequence of genetic materialmaterial

One plant the is commonly used in genetic and molecular One plant the is commonly used in genetic and molecular studies is studies is Arabidopsis thalianaArabidopsis thaliana

Arabidopsis thalianaArabidopsis thaliana is a small weed that is used as is a small weed that is used as a model organism in plant biologya model organism in plant biology

–– Model Organism Model Organism –– a species that is extensively a species that is extensively studied to understand particular biological studied to understand particular biological phenomenaphenomena

Studies of Studies of Arabidopsis Arabidopsis have helped to identify the have helped to identify the structure and function of many genes involved in structure and function of many genes involved in plant developmentplant development

The advantages of using this organism are The advantages of using this organism are

–– it has a small genome; ~ 26,000 genesit has a small genome; ~ 26,000 genes–– the complete DNA sequence is knownthe complete DNA sequence is known–– reproduces quickly reproduces quickly –– can be grown easily can be grown easily –– can reproduce as a hermaphroditecan reproduce as a hermaphrodite–– functions have been assigned to ~ 18,000 genesfunctions have been assigned to ~ 18,000 genes

Fig. 21-107

Understanding Gene ExpressionUnderstanding Gene Expression

Topic Primer 1Topic Primer 1

Understanding gene expression is Understanding gene expression is critical to understanding the role critical to understanding the role that molecular genetics plays in that molecular genetics plays in plant development.plant development.

Gene expression is defined as as Gene expression is defined as as the process by which a genes the process by which a genes DNA sequence is converted into DNA sequence is converted into the structures and functions of a the structures and functions of a cell.cell.

The Flow of Genetic InformationThe Flow of Genetic Information

–– The Central Dogma The Central Dogma ---- In order In order for genes to be expressed they for genes to be expressed they must first be transcribed into must first be transcribed into messenger RNA and then messenger RNA and then translated into proteintranslated into protein

DNADNAGenes are composed of DNAGenes are composed of DNA

DNA composed of nucleotides = DNA composed of nucleotides = nitrogenous base, phosphate group and nitrogenous base, phosphate group and sugar (ribose or sugar (ribose or deoxyribosedeoxyribose))

DNA is a double helix with sugarDNA is a double helix with sugar--phosphate backbones to outside and bases phosphate backbones to outside and bases to insideto inside

The bases of DNA are adenine (A), The bases of DNA are adenine (A), guanine (G), thymine (T) and cytosine (C)guanine (G), thymine (T) and cytosine (C)

Adenine must always base pair with Adenine must always base pair with thymine and guanine must always base thymine and guanine must always base pair with cytosinepair with cytosine

Thus one strand of DNA is the Thus one strand of DNA is the complement of the othercomplement of the other

Two strands are Two strands are antiparallelantiparallel meaning that meaning that if one has a 5if one has a 5’’ –– 33’’ polarity then the other polarity then the other has a 3has a 3’’ to 5to 5’’ polaritypolarity

DNA maintains the genetic code, this DNA maintains the genetic code, this code is transcribed into mRNAcode is transcribed into mRNA

mRNA holds the information for mRNA holds the information for making a polypeptide (protein) so it is making a polypeptide (protein) so it is said to said to ““code forcode for”” or or ““encodeencode”” a a polypeptidepolypeptide

mRNA has the same sequence as the mRNA has the same sequence as the nontemplatenontemplate strand except strand except uraciluracil (U) (U) substitutes for thymine (T)substitutes for thymine (T)

The strand that is complementary to The strand that is complementary to the mRNA is called the template, the mRNA is called the template, anticodinganticoding or or antisenseantisense strandstrand

The strand that has the same sequence The strand that has the same sequence as the mRNA is called the as the mRNA is called the nontemplatenontemplate, coding or sense strand, coding or sense strand

mRNAmRNA

ProteinsProteinsThe information contained in mRNA must be translated so that The information contained in mRNA must be translated so that proteins can be synthesizedproteins can be synthesized

Why are proteins important?Why are proteins important?

–– Provide structure that helps give cells integrity and shapeProvide structure that helps give cells integrity and shape

–– Serve as hormones to carry signals from one cell to anotherServe as hormones to carry signals from one cell to another

–– Bind and carry substancesBind and carry substances

–– Control the activity of genesControl the activity of genes

–– Serve as enzymes that catalyze essential chemical reactionsServe as enzymes that catalyze essential chemical reactions

ProteinsProteinsHow are proteins made?How are proteins made?

The information carried by the mRNA determines the The information carried by the mRNA determines the sequence of amino acids that will make up a sequence of amino acids that will make up a polypeptide chain (protein)polypeptide chain (protein)

Involves converting the nucleic acid languageInvolves converting the nucleic acid language””, of the , of the genetic code, to protein genetic code, to protein ““languagelanguage”” and is therefore and is therefore called translationcalled translation

The general rule is that each gene in the DNA gives The general rule is that each gene in the DNA gives rise to a single protein, there are however, exceptionsrise to a single protein, there are however, exceptions

During translation, the bases During translation, the bases of mRNA are read off in of mRNA are read off in groups of three, which are groups of three, which are known as known as codonscodons

Each Each codoncodon represents a represents a particular amino acidparticular amino acid

There are 64 different There are 64 different codonscodons in the genetic codein the genetic code

Some amino acids are Some amino acids are encoded by more than one encoded by more than one codoncodon

Codon Table

mRNA CodemRNA Code–– Base sequence: GAU Base sequence: GAU –– GCC GCC –– GUA GUA –– AUC AUC –– GAC GAC ––

UGUUGU

ProteinProtein–– 3 letter code: Asp Ala Val Ile As3 letter code: Asp Ala Val Ile Asp p CysCys

Gene MutationsGene MutationsGene mutations are defined as changes in the genetic material Gene mutations are defined as changes in the genetic material (DNA)(DNA)

Mutations can be caused by Mutations can be caused by

–– Copying errors that occur during cell divisionCopying errors that occur during cell division–– Exposure to radiationExposure to radiation–– Exposure to chemicals (mutagens)Exposure to chemicals (mutagens)

Gene mutations have varying effects on organisms depending Gene mutations have varying effects on organisms depending on whether the mutation alters the function of an essential or on whether the mutation alters the function of an essential or nonnon--essential gene productessential gene product

Gene mutations can be classified according to their structural Gene mutations can be classified according to their structural modifications; some examples aremodifications; some examples are

–– MissenseMissense mutationsmutations–– Nonsense mutationsNonsense mutations–– InsertionsInsertions–– Deletions Deletions –– FrameshiftFrameshift mutations mutations

The result of these mutations is a change in the protein productThe result of these mutations is a change in the protein product; the altered ; the altered protein may not function properlyprotein may not function properly

Note the following examples taken from the genetics home referenNote the following examples taken from the genetics home reference ce website, visit the website to review other examples of gene mutawebsite, visit the website to review other examples of gene mutationstions

–– http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/possiblemuhttp://ghr.nlm.nih.gov/handbook/mutationsanddisorders/possiblemutatitationsons

–– Link available on BlackboardLink available on Blackboard

MissenseMissense mutation mutation –– change in one DNA base pair change in one DNA base pair that results in the substitution of one amino acid for that results in the substitution of one amino acid for another in the protein made by the geneanother in the protein made by the gene

Insertion Insertion –– changes the number of DNA bases in a changes the number of DNA bases in a gene by adding a piece of DNAgene by adding a piece of DNA

Key Concepts Key Concepts –– Discussion 2Discussion 2Upon completion of this topic students should be able Upon completion of this topic students should be able to:to:

–– Explain the role molecular genetics plays in understanding Explain the role molecular genetics plays in understanding plant developmentplant development

–– Define the terms genotype, phenotype, gene expression, Define the terms genotype, phenotype, gene expression, wildwild--type, mutant and model organismtype, mutant and model organism

–– Describe the characteristics that make Describe the characteristics that make Arabidopsis thalianaArabidopsis thalianaa good model organism for plant developmenta good model organism for plant development

–– Explain the central dogmaExplain the central dogma–– Transcribe a gene sequenceTranscribe a gene sequence–– Translate a mRNA sequenceTranslate a mRNA sequence–– List the classifications of gene mutations and explain how List the classifications of gene mutations and explain how

these mutations affect translation (protein product)these mutations affect translation (protein product)