1、2022-8-16The Genetics of Mitochondria and Chliroplasts1Chapter 9The Genetics of Mitochondria and Chloroplasts2022-8-16The Genetics of Mitochondria and Chliroplasts2Chapter OutlineThe Classical Genetics of OrganellesThe Molecular Genetics of MitochondriaMitochondrial DNA and Human DiseaseThe Molecula
2、r Genetics of ChloroplastsThe Origin and Evolution of Mitochondria and Chloroplasts2022-8-16The Genetics of Mitochondria and Chliroplasts3Mitochondria,Chloroplasts,and the Biological Energy Wheel2022-8-16The Genetics of Mitochondria and Chliroplasts4The biological energy wheelCarl CorrensOne of the
3、three botanists who rediscovered Mendels Principles.2022-8-16The Genetics of Mitochondria and Chliroplasts5Section 1The Classical Genetics of OrganellesThe genetic material of organelles has been studied by tracing the inheritance of leaf pigmentation in plants,antibiotic resistance in algae,and met
4、abolic competence in yeast.2022-8-16The Genetics of Mitochondria and Chliroplasts6Most of the early studies were performed with plants,which possess both mitochondrial and chloroplasts.Consequently,it was not always possible to determine which of the two types of organelles was responsible for nucle
5、ar heredity.Later studies used yeast,for which the involvement of chloroplasts could be excluded.2022-8-16The Genetics of Mitochondria and Chliroplasts7The common precept shared by all of them is that organelle heredity does not follow simple Mendelian rules.Instead,it is characterized by unequal co
6、ntributions of the two parents and by an irregular segregation of alleles;that is,it violates Mendels Principle of Segregation.Organelle heredity is therefore non-Mendelian heredity.2022-8-16The Genetics of Mitochondria and Chliroplasts81.Leaf Variegation in PlantsThe leaves in plants sometimes exhi
7、bit a striking pattern of color variegation.Some sectors are green,others pure white.Intermediate shades of pale or yellow green may also exist.漂亮是大家想研究叶片花漂亮是大家想研究叶片花斑的一个原因斑的一个原因Leaf Variegation caused by the segregation of different types of chloroplasts.2022-8-16The Genetics of Mitochondria and Ch
8、liroplasts9Chloroplast sorting during mitosis.The irregular distribution of chloroplasts during cell division may produce a cell that lack chloroplasts capable of making chlorophyll.Through further divisions,such a cell will produce a white sector of tissue in an otherwise green leaf.2022-8-16The Ge
9、netics of Mitochondria and Chliroplasts10 Correns experiments on the inheritance of leaf variegation in Mirabilis(紫茉莉紫茉莉).(a)Green female X white male(on a variegating plant).(b)Green male X white female(on a variegating plant).2022-8-16The Genetics of Mitochondria and Chliroplasts11In mirabilis(紫茉莉
10、紫茉莉),the chloroplasts are transmitted to the offspring through the female reproductive cells but are largely,if not entirely,excluded from the male reproductive cells.When a plant inherits a mixture of pigmented and unpigmented chloroplasts from the female parent,its tissues may variegate because th
11、e two types of chloroplasts sort themselves out during development.2022-8-16The Genetics of Mitochondria and Chliroplasts12(天竺葵天竺葵)2022-8-16The Genetics of Mitochondria and Chliroplasts13This non-Mendelian,bipararental inheritance indicates that the color of Pelargonium(天竺葵天竺葵)leaves is determined b
12、y a mixture of maternal and paternal factors located outside the nucleus,presumably in the chloroplasts.It therefore seems that in the chloroplasts are transmitted through the pollen as well as through the ovule.PelargoniumPelargonium2022-8-16The Genetics of Mitochondria and Chliroplasts14The experi
13、ments of Correns and Baur demonstrated that leaf variegation is inherited as a non-Mendelian trait,one is that is almost certainly controlled by factors located in the chloroplasts.The discovery that chloroplasts contain DNA has made this hypothesis very attractive.Yet,in spite of the work of many s
14、cientists,the molecular basis of leaf variegation is still unknown.2022-8-16The Genetics of Mitochondria and Chliroplasts152.Antibiotic Resistance in Chlamydomonas(衣藻衣藻)Photosynthetic green algae are an important part of the biosphere.They are abundant in the oceans,where they form the foundation of
15、 the food chain,but they are also found on the land.2022-8-16The Genetics of Mitochondria and Chliroplasts16One terrestrial species,Chlamydomonas reinharditti,has been used extensively in genetic research.This unicellular,haploid organism exists in two different mating types,denoted plus and minus.C
16、ells of opposite mating type can fuse for produce a diploid zygote.The zygote then undergoes meiosis to produce four haploid offspring,which divide mitotically to produce clones of vegetative cells.2022-8-16The Genetics of Mitochondria and Chliroplasts17Analysis of these clones indicates that mating
17、 type is controlled by a nuclear gene with two alleles,mt+(specifying the plus mating type)and mt-(specifying the minus mating type).Two of the four offspring from a Chlamydomonas zygote are the therefore two mt+and two mt-.Many other nuclear genes with a Mendelian pattern of segregation have been i
18、dentified in Chlamydomonas.2022-8-16The Genetics of Mitochondria and Chliroplasts18Each haploid Chlamydomonas cell contains a single large chloroplast and several mitochondrial.When mt+and mt-cells fuse,their organelles are combined in the same diploid cell.It is not altogether clear what happens to
19、 these organelles inside the zygote,but when the four haploid offspring are produced,each has one chloroplast and several mitochondria.The basic number of organelles is therefore preserved.In 1954 Ruth Sager,an American geneticist,discovered that antibiotic resistance in Chlamydomonas is inherited a
20、s a non Mendelian trait.2022-8-16The Genetics of Mitochondria and Chliroplasts20This involved irradiating the mt+cells with UV light just prior to mating.When Sager mated irradiated mt+cells to unirradiated mt-cells,she found that some of the offspring inherited the cytoplasmic trait of the mt-paren
21、t instead of that of the mt+parent.These phenomena were finally explained when DNA was discovered in the Chlamydomonas chloroplast.2022-8-16The Genetics of Mitochondria and Chliroplasts21Both mt+and mt-cells possess this DNA,but when mating occurs,the DNA contributed by the mt-cell is degraded,proba
22、bly by a nuclease that specifically recognizes it.The offspring from a cross therefore retain only the DNA inherited from the mt+chloroplast.As a result,the trait encoded by this DNAand streptomycin resistance is one of themare always inherited through the mt+parent.2022-8-16The Genetics of Mitochon
23、dria and Chliroplasts22When mt+cells are irradiated prior to mating,the system that destroys the mt-chloroplast DNA is partially incapacitated.Consequently,some of the mt+chloroplast DNA survives and is transmitted to the offspring.This DNA may actually recombine with the mt+chloroplast DNA,generati
24、ng offspring that inherited chloroplast genes from both parents.2022-8-16The Genetics of Mitochondria and Chliroplasts23这是第一张非核这是第一张非核DNA的基因结构图的基因结构图A genetic map of chloroplast DNA in Chlamydomonas,based on the work of Sager and Ramains.Symbols:ac1,ac2,acetate requirement;sm4,streptomycin dependenc
25、e;nea,neamine resistance;sm3,low-level streptomycin resistance;sm2,high-level streptomycin resistance;ery,erythromycin resistance;spc,spectinomycin resistance;tm,temperature sensitivity.2022-8-16The Genetics of Mitochondria and Chliroplasts243.Metabolic Defects in YeastSome mutant strains of yeast f
26、orm tiny colonies when grown on a rich,glucose-containing medium.These strains are called petite mutants.Wild-type yeast strains form large,or grande colonies on glucose medium.Additional tests with different food sources suggest that petite mutants suffer from a defect in glucose metabolism.2022-8-
27、16The Genetics of Mitochondria and Chliroplasts25In many cases this defect is traceable to the mitochondria of the petite cells,which are ill-formed and lack many of the macromolecules found in wild-type mitochondria.These mitochondrial defects prevent petite cells from carrying out aerobic metaboli
28、sm.Boris Ephrussi2022-8-16The Genetics of Mitochondria and Chliroplasts26The neutral petite(中性小菌落中性小菌落)mutants are characterized by an inability to transmit the petite phenotype to the offspring of crosses with wild-type strains.When such crosses are performed,all four haploid offspring from a pair
29、of mated cells grow into grande coloniessuggesting that petite mutation has been lost.2022-8-16The Genetics of Mitochondria and Chliroplasts27By contrast,suppressive petite(抑制性小菌抑制性小菌落落)mutants are,under appropriate conditions,able to transmit the petite phenotype to all their progenysuggesting that
30、 the wild-type condition has been lost.With both types of mutants,reciprocal crosses between the mutants and wild-type strains give identical results;thus,the yeast mating types are not involved in the inheritance of the petite trait.2022-8-16The Genetics of Mitochondria and Chliroplasts28Non-mendel
31、ian segregation of(a)neutral and(b)suppressive petite mutation in yeast.2022-8-16The Genetics of Mitochondria and Chliroplasts29Inheritance of mt DNA in crosses between petite and wild-type strains of yeast.孢子形成孢子形成2022-8-16The Genetics of Mitochondria and Chliroplasts30What is the nature of the mtD
32、NA in suppressive petite mutants?Physical and chemical analysis has shown that it is a smaller DNA molecule than wild-type mtDNA and that is also very A:T-rich.These two features may endow the suppressive petite mtDNA with a explicative advantage over wild-type.However,a full understanding of why th
33、e suppressive petite DNA is effectively transmitted through crosses will require more research.2022-8-16The Genetics of Mitochondria and Chliroplasts31Key PointsOrganelle heredity is characterized by unequal parental contributions and by irregular phenotypic segregations.The non-Mendelian features o
34、f organelle heredity are due,in part,the preferential transmission of chloroplasts and mitochondria through the gametes of one sex,which in higher eukaryotes is usually the female.2022-8-16The Genetics of Mitochondria and Chliroplasts32Section 2The Molecular Genetics of MitochondriaMitochondria cont
35、ain DNA molecules with an assortment of genes.2022-8-16The Genetics of Mitochondria and Chliroplasts33Mitochondrial genetic systems consist of DNA and the molecular machinery needed to replicate and express the genes contained in this DNA.This machinery includes the macromolecules needed for transcr
36、iption and translation.Mitochondria even posses their own ribosomes.Many of these macromolecules are encoded by mitochondrial genes,but some are encoded by nuclear genes and are therefore imported from cytosol.2022-8-16The Genetics of Mitochondria and Chliroplasts341.Mitochondrial DNAMitochondrial D
37、NA(mtDNA)molecules vary enormously in size,from about 6 kb in malaria-causing parasite Plasmodium to 2500 kb in some of the flowering plants.Each mitochondrion appears to contain several copies of the DNA,and because each cell usually has many mitochondria,the number of mtDNA molecules per cell can
38、be very large.In a vertebrate oocyte:over 108 copiesIn a somatic cells:about 1000 copies.2022-8-16The Genetics of Mitochondria and Chliroplasts35Most mtDMA molecules are circular,but in some species,such as the alga Chlamydomonas reinharditii and the ciliate Paramecium aurelia(双小核草履虫双小核草履虫),they are
39、 linear.The circular mtDNA moleculaes appear to be organized in many different ways.MtDNA(yellow)in the unicellular organism Euglena gracilis.The nuclear DNA(red)is also visible.2022-8-16The Genetics of Mitochondria and Chliroplasts36In the vertebrates 37 distinct genes are packed into a 16-to 17-kb
40、 circle leaving little or no space between genes.In some of the flowing plants an unknown number of genes are dispersed over a large circular DNA molecule hundreds or thousands of kilobases in size.In these plants the mitochondrial genes may become separated onto different circular molecules by a pr
41、ocess of intramolecular recombination.动物动物mtDNA小，植物小，植物mtDNA大大2022-8-16The Genetics of Mitochondria and Chliroplasts37Intramolecular recombination in the mtDNA of the Chinese cabbage,Brassica campestris.Recombination between the repeated elements in the large circular DNA molecule partitions this mo
42、lecule into two smaller ones.Alternatively,the repeated elements in the two small molecules may recombine with each other to produce a single large molecule.2022-8-16The Genetics of Mitochondria and Chliroplasts38This recombination is mediated by repetitive sequences located in the mtDNA.An exchange
43、 between two of the repetitive sequences can partition the“master”mtDNA circle into two smaller circles,a process that superficially resembles the excision of a lambda prophage from E.coli chromosome.In some species,several DNA circles of different sizes are formed by recombination between pairs of
44、repetitive sequences located at different positions around the master DNA circle.2022-8-16The Genetics of Mitochondria and Chliroplasts39Animal mtDNA is small and compact.In human beings,the mtDNA is 16659 bp long and contains 37 genes,incl.2:rRNAs,22:tRNA,and 13:oxidative phosphorylation,the proces
45、s that mitochondria use to recruit energy.In mice,cattle,and frogs,the mtDNA is similar to that human beingsan indication of a basic conservation of structure within the vertebrate subphylum(脊椎动物亚门脊椎动物亚门).2022-8-16The Genetics of Mitochondria and Chliroplasts40Map of human mtDNA showing the pattern
46、of transcription.Genes on the inner circle are transcribed from the L strand of the DNA,whereas genes on the outer circle are transcribed from the H strand.The arrows show the direction of transcription.2022-8-16The Genetics of Mitochondria and Chliroplasts41Invertebrate mtDNA is about the same size
47、 as vertebrate mtDNA,but it has a somewhat different genetic organization.These differences seem to have been caused by structural rearrangements of the genes within the circular mtDNA molecules.2022-8-16The Genetics of Mitochondria and Chliroplasts42In fungi,the mtDNA is considerably larger than it
48、 is in animals.Yeast possesses circular mtDNA molecules 78 kb long.These molecules contain at least 33 genes,incl.2:rRNAs,23 to 25:tRNA,1:oxidative phosphorylation.The yeast mtDNA is larger than animal mtDNA because several of its genes contain introns and there are long noncoding sequences between
49、some of the genes.Animal mtDNA does not contain introns.2022-8-16The Genetics of Mitochondria and Chliroplasts43Plant mtDNA is much larger than the mtDNA of other organisms.It is also more variable in structure.One of the first plant mtDNA to be sequenced is from liverwort,Marchantia polymorpha(地钱地钱
50、).The mtDNA from this primitive,non-vascular plant(非维管植物非维管植物)is a 186-kb circular molecule with 94 substantial open reading frame(ORFs,开放阅读框开放阅读框),some corresponding to known genes and others having still unassigned genetic functions.2022-8-16The Genetics of Mitochondria and Chliroplasts44The latte
