#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.
In the discussion after McKelvie’s presentation,Rédei points out the difficulty of the job,& asks for more people to get involved in creating a map.However,his call went unanswered,& he was unable to get funding for this.Only 20 years later did Maarten Koornneef take up the work.
In the same discussion, Rédei also points out the availability of trisomic mutants which can be used to link linkage groups to chromosomes. Suzanne Lee-Chen & Lotti Steinitz-Sears from Rédei’s Department @Mizzou used these in 1967 to link 4 of Rédei’s 6 groups to chromosomes.
Koornneef built his own mapping work on their paper, and in 1979 finally linked Rédei’s 6 groups to the 5 chromosomes of Arabidopsis. Since starting his PhD-studies in @WURplant, Koornneef had isolated many more mutants & now incorporated them to create a more detailed map.
In the following years, Koornneef and his students continued to publish more detailed mapping results, analysis methods & marker stocks. Since Koornneef took on supervision duties for 31 students in his six years as PhD-student, he always had someone to help him.
Their work culminated in the full linkage map in 1983. Publishing it proved to be difficult though, as reviewers questioned the usefulness of the plant model,& the necessity of showing the recombination data, despite the journal publishing the same data for a mouse linkage map.
Despite this, the paper was published thanks to Koornneef’s “persuasive rebuttal letter”, which “felt like a personal victory for a young PhD student”. In 1987 he then added a line with 10 recessive markers spread over all chromosomes that could readily be used to map genes.
In 1988 the Meyerowitz lab added a restriction fragment length polymorphism map, which they later integrated with the linkage map. Koornneef, meanwhile, focused his attention on phytohormone mutants, as he had always considered the mapping more as “a teaching tool for students”.
However, 10 years later Koornneef’s interest in gene linkage was piqued again when he received Cape Verde islands (Cvi) Arabidopsis seeds from George Coupland. These lines were insensitive to day length, and also produced larger seeds than Landsberg ereceta.
So Koornneef initiated the crosses between the two lines, and suggested that his postdoc, Carlos Alonso-Blanco, could use these recombinant inbread lines to study natural variation in Arabidopsis. “This was the best advice I ever gave”, Koornneef recalls.
The work of Alonso-Blanco&Koornneef (re)started the research field of plant natural variation, which Arabidopsis pioneer Friedrich Laibach had previously initiated in the late 1930s,& this pioneering effort eventually led to Arabidopsis being one of the first organisms for GWAS.
It is amazing how this article, meant as“a teaching tool for students”, had such an enormous immediate AND long-term impact on the whole plant science field. See also: doi.org/10.1146/annure…
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:
#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.
Do you know Daisy Roulland-Dussoix? She is one of the discoverers of restriction enzymes, who’s findings paved the way for the development of recombinant DNA and cloning technologies. Accordingly, the finding was rewarded with a #NobelPrize. But the prize didn’t go to her... 🧵👇
Daisy Roulland-Dussoix worked with Werner Arber to study the mechanism for the observed host-specificity of λ Phages. It was known from an important 1953 paper (Bertani & Weigle) that phages, that had replicated in a certain E. coli strain, could only re-infect the same strain.
Roulland-Dussoix & Arber showed that host-specificity is linked with the phage’s DNA. Using phages carrying radiolabeled DNA, they showed that progeny with 2 parental DNA strands retained specificity, while progeny with newly synthesized daughter strands could adapt to new hosts.
#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.