Discover and read the best of Twitter Threads about #plantscienceclassics
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#PlantScienceClassics #18: Ethylene triple response mutants. 35 years ago Anthony Bleecker et al. exploited the triple response phenotype to identify the #ethylene receptor ETR1. The ethylene story is another example for #PlantBlindness @NobelPrize. doi.org/10.1126/scienc… 
Ethylene is a gaseous #phytohormone with a wide range of roles from plant development to immunity. Ernest Starling in 1905 defined a hormone as mobile chemical messenger synthesized by a multicellular organism, that has physiological activity distant from the site of synthesis.
The effect of ethylene on plants was first noted in the 1900s, when it leaked from illumination gas used in lamps and affected plants nearby. But it was Dimitry Neljubow, who in a series of experiments identified ethlyene as the active substance in the illumination gas in 1905.
#PlantScienceClassics #17: The Mildew Resistance Locus O (MLO). 80 years ago Rudolf Freisleben & Alfred Lein created the first powdery mildew resistant barley plant. 30yrs ago the gene was mapped, 25yrs ago cloned-yet it's mode of action remains a mystery. doi.org/10.1007/BF0148…
Powdery mildew is a fungal disease of many crop plants, most prominently maybe barley and wheat, where outbreaks can reduce grain quality & yield, and ruin complete harvests. Visible are the fluffy patches formed by the fungus (Blumeria graminis f. sp. hordei).
Freisleben used radiation-induced mutagenesis to create the barley 𝘮𝘭𝘰 mutant, which showed full resistant to this pathogen. A massive agricultural breakthrough!
See also Classic #2, to read about how Emmy Stein has developed this technique in 1921:
See also Classic #2, to read about how Emmy Stein has developed this technique in 1921:
#PlantScienceClassics #16: A linkage map of Arabidopsis thaliana. In 1983 the legendary Maarten Koornneef published a genetic map of A. thaliana, the basis for genetic work & an important contribution towards the acceptance of Arabidopsis as plant model. doi.org/10.1093/oxford…
In the early 1980s scientists finally adopted A. thaliana as model plant. At this point, several mutants were available, but their positions in the genome were mostly unknown. This was years before genome sequences became available,&genetic maps were still based on recombination.
Arabidopsis pioneer György Rédei did linkage analyses with 14 loci in the 1960s, but his genetic map from 1965 suggested 6 linkage groups – 1 more than chromosomes. Curiously, A. D. McKelvie created another map in parallel - & found 4 groups, 1 less than chromosomes.
#PlantScienceClassics #15 #PlantScienceFails #1: The auxin-independent (axi) Nicotiana tabacum lines. In 1992 Richard Walden et al. (specifically co-worker Inge Czaja) published activation-tagged axi protoplasts @ScienceMagazine that could divide&grow in the absence of any auxin!
The development of plant transformation in the early 1980s (classics #6&13) was inspirational for many scientists. Among them was Richard Walden, who teamed up with plant transformation pioneers Barbara & Thomas Hohn to leverage this advance to develop the “Agroinfection" method.
He then joined the next transformation pioneer, Jeff Schell, to develop more such tools. Their first was Activation-Tagging: 4 CaMV 35S enhancers (classic#9) were placed at the RB of the T-DNA. That way, they would overexpress the plant gene next to which the T-DNA was inserted.
#PlantScienceClassics #14: Mendelian inheritance. In 1866 Gregor Mendel published his work on dominant/recessive trait inheritance in peas, establishing the hereditary rules on which modern genetics is based. But nobody cared,& his scientific career ended. biodiversitylibrary.org/page/48299076
Mendel had always been interested in nature, and grew/kept and observed plants and bees in his parent’s garden. He later decided to become a monk and teacher. However, he failed teacher’s exam in 1850 & 1856, & eventually settled on being a monk and substitute teacher.
He satisfied his curiosity as a naturalist by keeping and observing plants and bees in the monastery garden, and eventually became interested in how traits are determined through generations. So he started to conduct crossing experiments with mice with grey or white fur.
#PlantScienceClassics #13: Floral Dip. Almost 25 years ago, in 1998, Steven Clough & Andrew Bent published their geniously simple Arabidopsis transformation protocol @ThePlantJournal: Dipping a plant upside down into Agrobacterium solution - et voilà! doi.org/10.1046/j.1365…
I have covered the plant transformation backstory in Classic#6, the T-DNA, so here I will focus on the events after 1983, the year plant transformation was established. These first transformants all were plants regenerated from cultured cells as calli.
Simply transforming an adult plant was not yet possible. One of the prerequisite toward this aim was the acceptance of Arabidopsis thaliana as a model plant (see also Classic#4), and the demonstration that A. thaliana was transformable via Agrobacterium.
#PlantScienceClassics #12: The stem cell-maintaining CLAVATA(CLV)-WUSCHEL(WUS) feedback loop. In 1999/2000 the labs of Elliot Meyerowitz & @simonrdg published 2 joint @ScienceMagazine papers describing a self-regulating signaling loop that maintains the stem cells of plants.
Plants continue to grow for their entire life due to the activity of stable pools of stem cells. The shoot apical #meristem (SAM) is the stem cell niche responsible for producing all above ground cells and is located at the tip of the plant’s stem.
The number of stem cells in the SAM is maintained constant, despite new formed cells continuously leaving the stem cell pool to build new tissues & organs. And like the stem cell number is stable, so are the number of organs formed, e.g. flower organs (see classic #1, ABC model).
#PlantScienceClassics #11: The GUS reporter system. In 1987 Richard Jefferson & colleagues from @michaelbevan565's lab published the first reporter system to monitor promoter activity in planta in the @embojournal: doi.org/10.1002/j.1460…
In the 1980s it was possible to express transgenes in cells of different organisms, but visualizing & assaying gene expression was still problematic. The lacZ β-galactosidase was a commonly used reporter, but compromised due to endogenous enzymes breaking down its substrates too.
So Jefferson developed the Escherichia coli uidA-encoded β-glucuronidase (GUS) reporter during his PhD in David Hirsh’s lab @CUBoulder. Adding a GUS-substrate to Caenorhabditis elegans carrying the GUS-reporter led to a colorful precipitate in all tissues with GUS expression.
#PlantScienceClassics #10: AuxREs, ARFs & Aux/IAAs. In 1997 the trifecta of Tim Ulmasov (TU), Gretchen Hagen (GH) & Tom Guilfoyle (TG) unleashed their @ScienceMagazine/@ThePlantCell double strike on the plant sciences, making auxin the hot topic of the field for the next decade.
Starting with Charles Darwin & son Francis in 1880, several scientists (J. Sachs, F. Went, N. Cholodny...) had speculated that there must be a mobile substance in plants, acting as messenger to direct growth in response to stimuli such as light or gravity (a ‘growth substance’).
In 1931 Fritz Kögl managed to isolate & describe this substance which he named 'auxin' (greek,‘to grow’). As it resembled animal hormones, he also proposed the name ‘phytohormones’ for this new group of plant substances. How this #Auxin promoted growth was not known yet, however.
#PlantScienceClassics #9: The CaMV 35S promoter. In 1985 Joan T. Odell & Ferenc Nagy from Nam-Hai Chua’s lab describe the Cauliflower mosaic virus 35S promoter @Nature, enabling researchers to ubiquitously expression their genes of interest in plants. doi.org/10.1038/313810…
The early 1980s were an important time for #PlantMolecularBiology: Among other things, plant transformation had just been established. But when introducing a gene into a plant, it requires regulatory sequences to activate its expression – and none active in plants were known.
In fact, the first transgenic plant published by the lab of Mary-Dell Chilton in 1984 in @CellCellPress had exactly this problem: They had introduced the yeast ADH1 gene without any regulatory sequences, and hence it was not expressed.
#PlantScienceClassics #8: Discoveries in Air. Joseph Priestley’s ‘Experiments and observations on different kinds of air’ in the 18th century formed the basis for the discovery and description of #photosynthesis. archive.org/details/experi…
Jan van Helmont was one of the first scientists who found that the mass of a plant is not acquired from the soil it grows in. When he grew a 5 lb willow tree in 200 lb of soil for 4 years, he found that the tree gained 164 lb, while the soil was only reduced by 2 lb.
But van Helmont concluded that the plant gained its mass solely from the water he added & neglected the air, despite being the person to first isolate & describe carbon dioxide, which he assumed was a different form of air, in the mid-17th century.
#PlantScienceClassics #7: The ZigZag Model.15 years ago @jonathandgjones & Jeff Dangl published their @nature review integrating Pattern/PAMP-Triggered Immunity (PTI) & Effector-Triggered Immunity (ETI) into one unified model of ‘The plant immune system’. doi.org/10.1038/nature…
In the 1980s, with plant molecular biology still in its infancy, the plant immune system was not understood very well at all. Dangl, at the time an immunologist working on mouse/human cells, remembers: ‘I had never considered that plants could recognize pathogens’.
But this fact, that the molecular mechanisms of the plant immune system were still basically a ‘black box’, is exactly what got Dangl interested and motivated to switch fields, and join the group of Klaus Hahlbrock at the @mpipz_cologne to work on plant immunity.
#PlantScienceClassics #6: The T-DNA. In a 1977 paper, Mary-Dell Chilton & colleagues identify the Transferred DNA (T-DNA), the bit of DNA that Agrobacterium tumefaciens inserts into the plant genome, to kick off the race toward the first transgenic plant. doi.org/10.1016/0092-8…
It was known since before the 1940s, that Agrobacterium could induce tumors (‘crown galls’) on plants, & that these tumors then grow autonomously of the bacterium, meaning that the plant had been permanently ‘transformed’. But the molecular details for the process were not known.
Armin Braun already speculated in 1947 that DNA may be involved in this transformation process. But research really took off in 1967, when Rob Schilperoort showed that Agrobacterium RNA could hybridize with crown gall DNA,indicating that bacterial DNA had indeed been transferred.
#PlantScienceClassics #5: “Jumping Genes”. In 1950 Barbara McClintock published her landmark @PNASNews paper on the #Maize Dissociation (DS) & Activator (Ac) #TransposableElements, revolutionizing the field of #Genetics to hostile opposition from her peers.doi.org/10.1073/pnas.3…
McClintock started her career & work on #Maize in the 1920s @Cornell, where she immediately made an impact by optimizing chromosome staining methods to characterize the chromosomes of triploid maize in 1929, & then describing the physical basis for chromosomal crossover in 1931.
In 1941 she relocated to @CSHL, where she worked on chromosome breaks in maize. When characterizing a specific break on chromosome 9, she noticed that the break was always associated with a locus she named Dissociation (DS), which could change its position on the chromosome.
#PlantScienceClassics #4: Arabidopsis thaliana suggested as model plant. In 1943 botanist Friedrich Laibach suggested A. thaliana as model organism for plant science. But the community was not ready yet - it took them another 40 years to see the light… doi.org/10.7287/peerj.…
Laibach started work on A. thaliana in 1907, when, for his PhD-thesis, he determined the number of chromosomes in different plants he collected around his hometown Limburg, or @UniBonn, where he worked. A. thaliana only had 5 chromosomes, one of the fewest he found.
In his 1943 paper, Laibach points out the benefits of working with A. thaliana, such as easy to grow, small genome, short lifecycle, high seed yield, can be crossed & mutated…), pointing out how comparable it is to the ‘prime example’ of models: #Drosophila melanogaster.
#PlantScienceClassics #3: The ligand-induced flg22/FLS2/BAK1 receptor-module. In a 2007 @Nature paper @delphinechinch1 et al. demonstrated that the bacterial flagellin22 triggers the formation of its own receptor-complex in plants, made up of FLS2 & BAK1: doi.org/10.1038/nature…
Already in 1999/2000, three papers from the legendary Boller-lab @UniBasel in @ThePlantJournal/@MolecularCell identified the elicitor flg22 & its receptor FLS2,laying the groundwork to establish Arabidopsis as a model system to study plant pathogen-interaction & immune-signaling.
But it was the addition of BAK1 as co-receptor, and the mechanistic finding that the ligand flg22 induces the formation of its own receptor-complex, which turned the flg22/FLS2/BAK1-module into the platform for countless new discoveries in the #MPMI/#PlantImmunity field.
#PlantScienceClassics #2: Radiation-induced mutagenesis. 100 years ago, in 1921, Emmy Stein developed radiation-induced #mutagenesis of #Antirrhinum majus plants. But today it seems that her invaluable contribution is being ignored… Read on doi.org/10.1007/BF0195…
Mutagenesis is now an invaluable tool to understand a gene’s function. In the early 1900s, when the hereditary substance was not even identified yet, it was an even more important tool, which Emmy Stein added to the small toolbox available to biologists at the time.
Stein used gamma rays from radium to irradiate both, adult plants & seeds, & showed the effects of different doses & different lengths, determining the lethal dose, &, importantly, the dose that induced weak mutants, that would still produce seeds to continue experimental work.
#PlantScienceClassics #1: The ABC model. 30 years ago, in 1991, plant science legends John Bowman, David Smyth and Elliott Meyerowitz published their groundbreaking paper on the ABC model in @Dev_journal: doi.org/10.1242/dev.11…
A regular Arabidopsis flower is composed of 4 whorls, each featuring specific organs: 4 sepals in the outer whorl, followed by 4 petals, then 6 stamen & 2 carpels in the inner whorl. These identities are controlled by the APETALA2 (AP2), PISTILLATA (PI) & AGAMOUS (AG) genes.
Mutant analysis of these genes showed that ap2 affects whorls 1 & 2 (Region A), pi affects whorls 2 & 3 (Region B), and ag affects whorls 3 & 4 (Region C). For their 1991 paper, the authors added the analysis of double and triple mutants of these three genes.
