Origin of the Taxa Examples of Protista

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Origin of the TaxaExamples of Protista

• Topic 6 BOT 3015

Bill Outlaw, Instructor
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Lecture Outline (a)
Chronology of life and life processes on
EarthPossible origins of the proto-eukaryal
cellEndosymbiosis and other methods for
non-vertical gene transferMorphology and
function of chloroplasts16(18)S rRNA sequence
analysisGreen AlgaeRed AlgaeHeterokonts (Brown
Algae and Oomycetes)
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Lecture Outline (a)
Chronology of life and life processes on
EarthPossible origins of the proto-eukaryal
cellEndosymbiosis and other methods for
non-vertical gene transferMorphology and
function of chloroplasts16(18)S rRNA sequence
analysisGreen AlgaeRed AlgaeHeterokonts (Brown
Algae and Oomycetes)
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Chronology (a-1)
BYBP
EVENT
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Chronology (a-2)
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Chronology (a-3)
BYBP
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Chronology (a-4)
BYBP
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Chronology (a-5)
BYBP
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Chronology (b-1)
BYBP
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Chronology (b-2)
BYBP
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Chronology (b-3)
BYBP
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Chronology (b-4)
BYBP
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Chronology (b-5)
BYBP
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Chronology (b-6)
BYBP
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Chronology (b-7)
BYBP
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Chronology (b-8)
BYBP
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Schopf and His Fossils
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Microfossils (3.5 BYBP, Australia)
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Lecture Outline (b)
Chronology of life and life processes on
EarthPossible origins of the proto-eukaryal
cellEndosymbiosis and other methods for
non-vertical gene transferMorphology and
function of chloroplasts16(18)S rRNA sequence
analysisGreen AlgaeRed AlgaeHeterokonts (Brown
Algae and Oomycetes)
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Origin of the Major Groups (a)Bacteria, Archaea,
Eukarya
1. An unknown protobiont evolved two
lineagesone leading to Bacteria and a second
leading to the progenitor of Archaea and Eukarya.
Or, . . .
Credit Andrew White, Staffordshire University,
UK
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Origin of the Major Groups (b-1)Bacteria,
Archaea, Eukarya
?
Archaeaon
Bacterium
2. Bacteria and Archaea arose (either
independently or from a single unknown ancestor).
A single Bacterial cell fused with a single
Archaeal cell, creating the proto-eukaryal cell.
Whole-cell Fusion
Proto-eukaryal cell
idea from Lynn Margulis
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Origin of the Major Groups (b-2)Bacteria,
Archaea, Eukarya
Whole-cell Fusion
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Origin of the Major Groups (c)Bacteria, Archaea,
Eukarya
Summary Both explanations are essentially based
on inferences from present-day organisms. Both
explanations have strong advocates. Interpretation
s must have reservations. (For example,
whole-cell fusion, a common ancestor, or lateral
gene transfer could account for a trait in
Eukarya.)
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Lecture Outline (c)
Chronology of life and life processes on
EarthPossible origins of the proto-eukaryal
cellEndosymbiosis and other methods for
non-vertical gene transferMorphology and
function of chloroplasts16(18)S rRNA sequence
analysisGreen AlgaeRed AlgaeHeterokonts (Brown
Algae and Oomycetes)
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Phagocytosis as a means of horizontal gene
transfer.
In part, as a lead-in to endosymbiosis . . . .
PNAS 100 7419
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Basic Outline of (Primary) Endosymbiosisusing
the plastid as an example
The bulk of evidence (more later) indicates that
all chloroplasts resulted from a single primary
endosymbiotic event (monophyletic origin of
plastids).
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Basis for the Endosymbiosis Mechanism (a)
In virtually all ways chloroplasts
mitochondria bacteria
size
ribosomes size sensitivity antibiotics
(implying homologous function)/translation
DNA packaging/transcription
. . . and other features such as bias towards
certain lipids in membranes
. . . and, as expected, all the above being in
agreement with sequence data (more later)
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Basis for the Endosymbiosis Mechanism (b)
In virtually all ways chloroplasts
mitochondria bacteria . . .but they are not
identical
DNA-containing organelles are only
semiautonomous For example, a chloroplast may
contain 100 ORF, but requires 1000 polypeptides
for function. (Some of the missing genes were
transferred to the nucleus and somebeing
redundant with those of the hostwere lost.)
loss of function/features (e.g. cell wall) is
the rule (again, a reason for loss of genes).
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EndosymbiosisThe devil is in the details.
The details . . .
all chloroplasts are not the same. (more later)
all mitochondria are not the same. For
example, the typical mammalian mitochondrial
genome has only 0.017 MB, but those of some plant
mitochondria have up to 2.5 MB.
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Secondary Endosymbiosis
At least three separate secondary endosymbiotic
events led to plastids in different groups of
algae. Some odd algae even have two kinds of
chloroplastseither from tertiary endosymbiosis
or serial acquisition of chloroplasts.
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EndosymbiosisSummary and BOT 3015 Focus
Primary
Secondary
Expert opinion, but not inclusive of all opinions.
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Gene transfer . . . Summary (a)
The historical way to think of gene transfer is
vertically 1. Asexual (e.g., division of a
single-celled organism to form two daughter
organisms by mitosis) 2. Sexual (i.e., formation
of gametes followed by syngamy)
In this historical way of thinking, gene transfer
is linear. One can thus construct a tree in
which there are unambiguous lines of descent.
--------------------------------------------------
------------------------- Life is not so simple
because of horizontal (lateral) gene transfer.
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Gene transfer . . . Summary (b)
Mechanisms for horizontal gene transfer
conjugation, phagocytosis, endosymbiosis (as
shown earlier)
bacterial transformation (uptake of naked
DNA). Natural (complex cell machinery required)
and artificial (e.g., by treatment with
membrane-permeabilizing agent) more later
bacterial transduction (gene introduction by
virus)
Transformation is used broadly in most
genetic engineering literature to mean a stable
change in genetic potential. In plants, e.g.,
introduction of a novel gene is usually
accomplished by (a) transfer of a gene via a
recombinant plasmid from the crown gall
bacterium, Agrobacterium (b) biolistics (gene
gun) electroporation or chemically induced
membrane pores (d) microfibers (stabbing cells
with gene-coated fibers.)
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Gene transfer . . . Summary (c)
How important is gene-by-gene horizontal gene
transfer in evolution?
central force of evolution of many different
prokaryotes.
occurs across domains
role in eukaryotes less certain, but evidence
is accumulating in some groups, particularly
phagocytotic algae. (E.g., in one study, 21 of
nuclear genes for plastid-targeted proteins were
derived by horizontal gene transfer.)
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Lecture Outline (d)
Chronology of life and life processes on
EarthPossible origins of the proto-eukaryal
cellEndosymbiosis and other methods for
non-vertical gene transferMorphology and
function of chloroplasts16(18)S rRNA sequence
analysisGreen AlgaeRed AlgaeHeterokonts (Brown
Algae and Oomycetes)
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Chloroplasts are one kind of plastid
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Green Algal and Plant Chloroplast
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Chloroplast Types (a)
Red Algae (most similar to Cyanobacteria)
Brown Algae (and others) (example of heterokont
meiotic gametogenesis)
Cryptomonad (convincing example of surviving
nucleomorph)
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Organization of PS II light-harvesting pigments
Three types of antenna complexes involved in
light harvesting.
phycobilisomes, cyanobacteria and red algae
LHCII (chl a/b binding), plants green algae
fucoxanthin/chl a/c complex, brown algae
Core Complex The above two complexessufficient
for photosynthesis. Essentially the same in all
photosynthetic eukaryotes.
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Organization of PS II light-harvesting pigments
Three types of antenna complexes involved in
light harvesting.
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Lecture Outline (e)
Chronology of life and life processes on
EarthPossible origins of the proto-eukaryal
cellEndosymbiosis and other methods for
non-vertical gene transferMorphology and
function of chloroplasts16(18)S rRNA sequence
analysisGreen AlgaeRed AlgaeHeterokonts
(Brown Algae and Oomycetes)
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Plastidic and other 16S rRNA phylogeny
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18S rRNA phylogeny
Plants and Green Algae
Animals and Fungi
Phototrophic Heterotrophic Heterokonts
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Summary of Relationships
Chloroplasts have a monophyletic origin (All
plastidic16S rRNA sequences more similar to each
other than to any extant cyanobacterium gene
clusters in chloroplasts similar to each other
but different to cyanobacteria similarity of
protein import machinery)
Green Algae and plants share a recent common
ancestor not shared by other groups (chloroplast
structure, chemistry, 16S 18S rRNA sequences)
The eukaryotic portions of heterokonts share a
common history, regardless of whether
photosynthetic or not (morphology, 18S rRNA
sequence, much more)
Fungi and animals share a recent common
ancestor not shared by other eukaryotes (18S rRNA
and much more)
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Diversification of plastids
The large diversity of plastids, assumed to have
been achieved since the seminal endosymbiotic
event, obviously raises questions because no
single extant cyanobacterium contains the range
of light-absorbing pigments found in algae.
. . . but the biosynthetic pathways leading to
pigments are similar, and, moreover, the
engulfed cyanobacterium might have had the range
of pigments, which have been subsequently lost.
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Lecture Outline (f)
Chronology of life and life processes on
EarthPossible origins of the proto-eukaryal
cellEndosymbiosis and other methods for
non-vertical gene transferMorphology and
function of chloroplasts16(18)S rRNA sequence
analysisGreen AlgaeRed AlgaeHeterokonts
(Brown Algae and Oomycetes)
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Examples of Green Algae Colonial Forms
These panels depict three species (Gonium,
Pandorina, Eudorina) that comprise a colonial
series made up of Chlamydomonas-type cells. The
pinnacle in this dead-end evolutionary series is
Volvox, which is made of thousands of cells.
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Examples of Green Algae Siphonous Form
Acetabularia
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Examples of Green Algae Parenchytamous Forms
Ulva
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Chlamydomonas sp.
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Chlamydomonas asexual life cycle
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Chlamydomonas sexual life cycle
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Lecture Outline (g)
Chronology of life and life processes on
EarthPossible origins of the proto-eukaryal
cellEndosymbiosis and other methods for
non-vertical gene transferMorphology and
function of chloroplasts16(18)S rRNA sequence
analysisGreen AlgaeRed AlgaeHeterokonts
(Brown Algae and Oomycetes)
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Examples of Red Algae Bonnemaisonia
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Examples of Red Algae coralline alga (calcified
walls)
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Examples of Red Algae Batrachospermum
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Lecture Outline (h)
Chronology of life and life processes on
EarthPossible origins of the proto-eukaryal
cellEndosymbiosis and other methods for
non-vertical gene transferMorphology and
function of chloroplasts16(18)S rRNA sequence
analysisGreen AlgaeRed AlgaeHeterokonts
(Brown Algae and Oomycetes)
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Heterokont (different flagella)
Image from Graham Wilcos
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Examples of Brown Algae Durvillea, New Zealand
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Examples of Brown Algae Laminaria
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Examples of Brown Algae Macrocystis
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Examples of Brown Algae Fucus (Rockweed)
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Fucus sexual life cycle
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Phytophthora infestans on potato
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Phytophthora life cycle
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