Integrative systems in plants

"intro textbook-type background" (Chap 35 in 3rd edition, 39 in 6th)

"motor" movements - fast, action potentials
fast movements-turgor changes-mimosa
also Venus fly trap
not so fast, introduce "tropism"
geotropism (gravitropism)
also "sensory"
statoliths in cells
geotropism (gravitropism)

HORMONES

TRANSPARENCY (new) shows molecules
Auxins indole (3 acetic acid)
phototropism - Darwin expts.communication with tip for grass to grow
to light TRANSPARENCY
Went 1927 agar expts TRANSPARENCY
make cells grow more
apical dominance (pinch back flowers)
polar transport (active) from apical meristem of terminal bud
rooting hormones
Weed-be -Gone, Ortho, Scotts plus 2, 2,4-D; weed and feed, deadly agent orange
used to have 2,4,5-T but this was contaminated with dioxin
monocots resist, works on dicots, broad leafed

Ethylene - ripen fruit - kerosene heaters, blueberies, fruit rots
dropping of leaves in deciduous perennials
TRANSPARENCY (new) effects of ethylene in mutanta, seedlings

Cytokinins - contain adenine coconut milk- cell division
Miller expts on aged herring sperm - degraded DNA
interact with auxin in callus vs. root
" " " in apical dominance
Gibberellins - cell elongation - dwarf corn and peas lack
foolish [rice] seedling disease fungus
flower earlier, better Thompson seedless grapes
barley (cereal) seed germination - break dormancy
mRNA for a-amylase act through 2nd messenger
involved in "bolting" with huge internode
Abscisic acid - inhibit growth prepare for winter
rain washes out of desert seed thus germinate

Phytochrome - photodormant lettuce seeds germ after 660,
not 730 - also photomorphogenesis
TRANSPARENCY (new) dimer of photoreceptor with chromophore plus kinase
photoperiodism - dark period important
Pr->Pfr
daylight hits red, slow reconversion TRANSPARANCY
long short day plants
TRANSPARENCIES red and far red in flowering
TRANSPARENCY (new) phytochrome signalling via G protein, calmodulin, transcription factors
Florigen - timing of flowers in short and long day plants
In Summary, there are signal transductions in plants
TRANSPARENCY

Recent work
A. M. Jones, Surprising signals in plants (perspectives) Science 263 183-184, 1994
TRANSPARENCY
Salicylic acid
SAR = systemic acquired resistance, local pathogen->whole plant
bind catalase gets rid of ROS (reactive oxygen species)
turns on pathogenesis related genes
Ethylene
Etr gene homology with prokaryotic two-component signal system
downstrean CTR1 is like Raf serine-threonine protein kinase
Blue light
phototropism (growth)
receptor should be flavoprotein
hy4 mutant is insensitive
use T-DNA to find a tagged allele to get gene
like a prokaryotic flavoprotein that repairs UV damage (photolyases)
Auxin
not expect mutants since auxin is so important
axr1 has same amount of auxin so it is receptor
clone - AXR1 is like E1, an enzyme involved in ubiquinization
rapid turnover of short-lived transcription factors

S. Cutler et al., A protein farnesyl transferase involved in abscisic acid signal transduction in Arabidosis. Science 273 1239-1241, 1996
sesquiterpine which arrests growth, controls stomata and seed dormancy
secondary messengers like IP3 and Ca2+ are involved
Arabidosis thaliana abi gene reduce sensitivity -
serine-threonine phosphatase
transcriptional activator
seek enhanced response genes (era) (less ABA to inhibit seed)
transferred DNA method (T-DNA) allows isolation of genomic region
era1 13 introns - 404 a.a. like beta subunit of farnesyl transferase
add near COOH-terminal at a CaaX motif
note that Ras and gamma of heterotrimeric G protein are farnesylated (for membrane localization - recall paper about ras in cancer lecture)
also rhodopsin kinase must be farnesylated to attenuate receptor activation

J. Q. Wilkinson et al., An ethylene-inducible component of signal transduction encoded by Never-ripe. Science 270 1807-1809, 1995.
ethylene C2H4 - seed germination, flower initiation, fruit ripening, tissue senescence,
organ abscission
Never-ripe (Nr)
CTR1 gene is serine-threonine kinase like Raf kinase
ETR1 encodes membrane protein which dimerises and binds ethylene (receptor)
Nr is mutant of new gene (TXTR-14) encodes 635 aa, 71 kD
lacks C-terminal 103 aa of ETR1
sensor histidine kinase
Nr has C->T at nucleotide 411 => Pro -> Leu

G. E. Schaller & A. B. Bleecker, Ethylene-binding sites generated in yeast expressing the Arabidopsis ETR1 gene, Science 270 1809-1811, 1995
ETR1 seems to be ethylene receptor 14 C binding studies, expression in yeast.
mutants are insensitive to ethylene. etr1-1 mutant has no binding
Cys65->Tyr => metal coordination (Cys, His Met)
ETR1 gene cloned N-terminal is for membrane localization
C-terminal is like histidine kinase of bacteria
(total is 738 amino acids), dimer with disulfide bonds
hard to reconcile with tomoto homologue Never-ripe
in terms of if receptor is inactive or active with ethylene

J. Marx. Plants, like animals, may use peptide signals (research news), Science 273 1338-1339, 1996 Previously thought that the cell wall was too thick for peptides
1991 systemin to fight off insect pests
ENOD40 (ENOD gene = early nodulation) regulates formation of root nodules (for nitrogen fixation in legumes)
release cells from growth inhibition - makes auxin tolerant
real odd: ORF = 12 or 13 a.a. (in animals, peptides cleaved from precursor)
another gene - Crinkly abnormalities in corn leaf and seed
like receptor for tumor necrosis factor, that peptide being 157 aa
cr4 mutant cloned => receptor kinase
Xa21 is receptor kinase gives resistance in rice to bacterial pathogen
S = self-incompatability another receptor kinase in some plants
pistol recognizes signal on pollen

B. Lacombe et al., The identity of plant glutamate receptors, Science 292, 1486-1487, 2001
In animals, glutamate receptors are ligand gated channels.
There are 20 glutamate receptors in plants in 3 clades.
Some similarity with those of animals, but not much.May be involved in light signal transduction or Ca2+ homeostasis.

R. Hooley, Plant steroid hormones emerge from the dark (comment), Trends in Genetics 12 281-283, 1996
Brassica (mustards, cauliflowers, cabbages, turnips)
brassinosteroids discovered as a growth stimulator from pollen
works in light, not in dark (hence title of paper)
stimulate cell elongation and division (interaction with auxin)
etoliation fast growth underground then photomorphogenesis (make photosynthetic pigments)
there are mutants
TRANSPARENCY -
steroid synthesis:determine which replacements rescue
Arabidopsis DET2 gene and det2 mutation homology with 5 alpha-reductase
use T-DNA technique Agarobacterium tumefaciens transferred DNA insertion
cpd mutant of CPD gene and tomato Dwarf homology to steroid hydroxylase
dim several possible homologies
also insensitive mutants: cbb2 and bri1 receptor or post brassinolide conversion

J. Li et al., A role for brassinosteroids in light-dependent development of Arabidosis, Science 272, 398-401, 1996
also
D.W.Russell, Green light for steroid hormones, Science 272, 370, 1996
mutants of Arabidosis that seem light grown even if grown in dark
DET2 codes for 262 amino acid like mammalian 5alpha-reductase
several types of mutants, but, importantly, glutamate->lysine at 204
using NADPH, in mammals, testosterone->dihydrotestosterone
hereditary male pseudohermaphroditism from equivalent glutamate ->aspartate at 197
from campesterol to brassinolide, 10 steps, DET2 may be 1->2, CPD may be 5->6

Z. He et al., Perception of Brassinosteroids by the extracellular domain of the receptor kinase BRI1, Science, 288, 2360-2363, 2000
In animals, there are RTKs
In plants, they are always serine-threonine kinases and they are called RLKs (receptor-like kinases).
Steroids perdeived at membrane

J. Li and K. H. Nam, Regulation of brassinosteroid signalling by a GSK3/SHAGGY-like kinase, Science 295, 1299-1301, 2002
GSK3/SHAGGY is serine-threonine kinase (Recall the Wnt pathway.)
There are some in plants (10 in Arabidopsis).
BIN2 (brassinosteroid insensitive encodes a GSK3/SHAGGY kinase

J. Gewolb How seedlings see the light, Science 293, 1237-1238, 2001
photomorphogenesis
COP1 cause degradation of transcription factors
blue receptors are cryptochromes and they interact with COP
phytochromes may interact with cryptochrome

S. Ikeda et al., An aquaporin-like gene required for the Brassica self-incompatibility response. Science 276, 1564-1566, 1997
Brassica - self-pollination always inhibited in field of wild mustard, cross pollination usually works.
Self-incompatibility insures cross-polination, pollen tube development is disrupted
Background:
There is a cluster of genes at the S locus
ligand on pollen interacts with receptor tyrosine kinase -> phosphorylation cascade in the stigma's epidermal cell to "reject" pollen
New work:
outside S locus, mod mutation affects
probe shows mRNA in MOD/MOD, much less transcript in mod/mod, so allele is hypomorphic
286 aa like MIP (major intrinsic protein) like aquaporin, 6 membrane spanning
(see channel lecture, Dean et al. paper)

A. Kachroo et al. Allele-specific receptor-ligand interactions in Brassica self-incompatibility, Science293, 1824-1826, 2001
serine-threonine kinase (SRK) in stigma
cysteine-rich peptide (SCR) in pollen binds SRK

(The following was covered in channels, so it won't be repeated here.)
R. Hedrich & P. Dietrich, Plant K+ channels: similarity and diversity, Bot. Acta. 109, 1-8, 1996
This paper refers to "green" (from plants) and "red" (from animals)
this work is electrophysiological, and application of the patch clamp has contributed greatly
Of course, nutritionally, for plants and herbivores, potassium is very relevant (macronutrient)
several rapid volume change responses
for instance, here is a TRANSPARENCY from this department's introductory biology text to show the involvement of K+ in guard cell responses, responsible for opening and closing of stomata
an overall outline:
Inward rectifying voltage dependent K+ channels for K+ uptake
Outward rectifying voltage dependent K+ channels for K+ release
Also there is a high affinity K+ transporter (HKT1) about which little is known though it is thought that protons are cotransported. Such a system would be used to get K+ in from low concentration in soil.
This paper concentrates on uptake channels like those cloned from:
Arabidosis thaliana (KAT1)
Solanum tuberosum (KST1)
channel conductance is 5-30 pS
for a 10 x change in K+ gradient, voltage changes 56-58 mV in accord with the Nernst potential (see earlier this semester, discussion of Paramecium)
not many insect, scorpion, snake, frog or dinoflagellate toxins which affect animal channels affect plant channels
But external Cs+ and TEA+ do block, but weakly
In contrast with animal channels, KST1 and KAT1 have ATP and cyclic nucleotide cassettes and several channels are ATP dependent
Like shaker in S1-S6 and H5 or P (pore forming) - TRANSPARENCY with 21 conserved amino acids except that plant channel has extra 14 amino acids
No N-terminal ball and chain and no inactivation
there are AKT1 = Arabidosis K+ transporters which have ankyrin binding domains

E. Pennisi, Plants decode a universal signal (Research News) Science 278, 2054-2055, 1997
also
Y. Wu et al., Abscisic acid signaling through cyclic ADP-ribose in plants, Science 278, 2126-2130, 1997
TRANSPARENCY
abscisic acid (ABA) turns on stress responsive genes (stress = cold, drought and salinity)
acts through releasing calcium in burst from intracellular stores
in humans, disorders in cyclic ADP-ribose signaling -
heart arrythmias (bad contractions if too little calcium)
and diabetes (glucose-stimulated insulin release from pancreas)
the assay is the stress genes which ABA turns on --
rd29A (dessication-responsive gene)
and kin (cold-inducible gene)
a control gene was turned on by calcium but not by cADPR
another interesting control - IP3 could turn on genes. heparin blocks this but not if ABA turns on genes implicating another signaling pathway
may also be involvd in closing of stomata in response to drought
3 ways calcium may be regulated: (1) IP3, (2) cADPR, and (3) nicotinic acid adenine dinucleotide phosphate (NAADP+) [For (2) and (3), receptor is not known.]
ryanodine receptor (RyR) may be receptor for cADPR

H. Ullah et al., Modulation of cell proliferation by heterotrimeric G protein in Arabidopsis, Science 292, 2066-2069, 2001
X-Q Wang et al., G protein regulation of ion channels and abscisic acid signaling in Arabidopsis guard cells, Science 292, 2070-2073, 2001
BEEllis and GFMiles One for all? (Perspectives) Science 292, 2022-2023, 2001
TRANSPARENCY
G protein - mammal genomes have 20 alpha, 5 beta and 12 gamma, plants 1:2(?):1
silence GPA1 indicates that auxin acts through Galpha (in part), also abscisic acid's closing of stomata

E.M.Meyerowitz, Plants compared to animals: The broadest comparative study of development, Science 295, 1482-1485, 2002
If common ancestor were unicellular (very probable), development should be very different
TRANSPARENCY
2.7 billion years ago, eukaryotes split off
After that, mitochondria become intracellular symbiotes ("uptake of alpha proteobacterium")
1.6 billion years ago, last common ancestor of plants and animals
After that, chloroplasts become intracellular symbiotes ("uptake of cyanobacterium")
0.6 billion years ago, multicellular plants and animals (but fossil record is not complete)
Animals - "spatially specific transcriptional activation of master regulatory genes, the HOX homeobox genes"
Plants - "master regulatory genes are transcriptionally activated in a radial pattern" (for "radial pattern of floral development") but for plants, MADS box (no homology to HOX)
EGF (receptor tyrosine kinase) in Ras pathway important in Drosophila development, but Arabidopsis genome has no RTK or Ras.
Others (like I-kappa B, NF-kappaB, SMADs) have no relatives in Arabidopsis.
No nuclear receptors, Smo, Ptc, Notch in plants
Processes are similar, but genes are not homologous. (convergent evolution)
There is cell-cell signalling similar to boss-sev in shoot apical meristem (CLAVATA3 is ligand, CLAVATA1 is receptor).
Plants have important domains like serine/threonine kinases and leucine-rich repeats, but organization is different.
Plant steroid receptors are different from animal nuclear receptors - leucene rich-repeat receptor kinase.
Ethylene inactivates receptors. 5 receptors like bacterial receptors. At least one is histidine kinase like in bacteria. Act through Raf (MAPKKK)
5 phytochrome genes in plants homologous with cyanobacterial except serine/threonine kinase instead of histidine kinase.Probably horizontal transfer from uptake of protochloroplast.

References:

S. Cutler et al., A protein farnesyl transferase involved in abscisic acid signal transduction in Arabidosis. Science 273 1239-1241, 1996

J. Gewolb How seedlings see the light, Science 293, 1237-1238, 2001

Z. He et al., Perception of Brassinosteroids by the extracellular domain of the receptor kinase BRI1, Science, 288, 2360-2363, 2000

R. Hooley, Plant steroid hormones emerge from the dark (comment), Trends in Genetics 12 281-283, 1996

S. Ikeda et al., An aquaporin-like gene required for the Brassica self-incompatibility response. Science 276, 1564-1566, 1997

A. M. Jones, Surprising signals in plants (perspectives) Science 263 183-184, 1994

A. Kachroo et al. Allele-specific receptor-ligand interactions in Brassica self-incompatibility, Science293, 1824-1826, 2001

B. Lacombe et al., The identity of plant glutamate receptors, Science 292, 1486-1487, 2001

J. Li et al., A role for brassinosteroids in light-dependent development of Arabidosis, Science 272, 398-401, 1996
also
D.W.Russell, Green light for steroid hormones, Science 272, 370, 1996

J. Li and K. H. Nam, Regulation of brassinosteroid signalling by a GSK3/SHAGGY-like kinase, Science 295, 1299-1301, 2002

J. Marx. Plants, like animals, may use peptide signals (research news), Science 273 1338-1339, 1996

E.M.Meyerowitz, Plants compared to animals: The broadest comparative study of development, Science 295, 1482-1485, 2002

E. Pennisi, Plants decode a universal signal (Research News) Science 278, 2054-2055, 1997
also
Y. Wu et al., Abscisic acid signaling through cyclic ADP-ribose in plants, Science 278, 2126-2130, 1997

G. E. Schaller & A. B. Bleecker, Ethylene-binding sites generated in yeast expressing the Arabidopsis ETR1 gene, Science 270 1809-1811, 1995

H. Ullah et al., Modulation of cell proliferation by heterotrimeric G protein in Arabidopsis, Science 292, 2066-2069, 2001
X-Q Wang et al., G protein regulation of ion channels and abscisic acid signaling in Arabidopsis guard cells, Science 292, 2070-2073, 2001
BEEllis and GFMiles One for all? (Perspectives) Science 292, 2022-2023, 2001

J. Q. Wilkinson et al., An ethylene-inducible component of signal transduction encoded by Never-ripe. Science 270 1807-1809, 1995.

This page was last updated on April 30, 2002

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