Arabidopsis Research Roundup: August 23rd

There is a bumper crop of papers in this weeks UK Arabidopsis Research Roundup! First up is a remarkable piece of work from George Bassel’s (University of Birmingham) lab that defines the network of cellular interactions that occur in the hypocotyl. Second and third are papers from the JIC in which Lars Ostergaard’s group uncovers the extent of the ETTIN signaling network and Caroline Dean‘s and Martin Howard’s labs provide evidence for a two step progression toward stable gene silencing following vernalisation at the FLC locus. Fourthly is a study that includes members of Alex Webb’s group (University of Cambridge) as co-authors that investigates the link between the circadian clock and night time starch metabolism. Fifth is a paper from Christine Foyer (University of Leeds) that looks at the effect of commonly used inhibitors on cellular redox state and gene expression. The next paper includes Phillip Carella (SLCU) as a co-author and looks at the role of classic flowering time genes on the phenomenon of Age-Related Resistance and finally Lee Sweetlove’s (University of Oxford) lab has published a methods paper for the analysis of photorespiration in non-photosynthetic tissues.

Jackson MD, Xu H, Duran-Nebreda S, Stamm P, Bassel GW (2017) Topological analysis of multicellular complexity in the plant hypocotyl. Elife http:/​/​dx.​doi.​org/10.7554/eLife.26023

Open Access

George Bassel (University of Birmingham) is the corresponding author on this work that provides fantastic images of the plant hypocotyl taken as part of an analysis on the cell growth dynamics in this organ. They show that Arabidopsis epidermal atrichoblast cells demonstrate a reduced path length that coincides with preferential movement of small molecules through these cells. They analysis this process in various mutants showing which gene activities were necessary for the construction of this pattern. In addition they compared topological features in Arabidopsis, Poppy and Foxglove, showing that cell interactions and path length determinants differ between these organisms. Overall this manuscript defines the network principles that control complex organ construction as well as a function for higher order patterning.

Simonini S, Bencivenga S, Trick M, Ostergaard L (2017) Auxin-Induced Modulation of ETTIN Activity Orchestrates Gene Expression in Arabidopsis. Plant Cell 10.1105/tpc.17.00389

Open Access

Last year Lars Ostergaard (JIC) discussed a paper from his lab on the GARNet YouTube channel in which they defined a new auxin-signaling paradigm that involved the non-canoical Auxin Response Factor ETTIN. This follow up to that study investigates the genetic network controlled by ETTIN activity and defines a range of developmental processes dependent on ETTIN auxin sensing. Furthermore by looking at direct ETTIN targets they suggest that this protein acts as a central node for the coordination of auxin signaling in the shoot. Finally their analysis of the effect of auxin on interactions between ETTIN and other transcription factors indicates that these are important factors in the diverse set of growth process controlled by auxin.

Yang H, Berry S, Olsson TSG, Hartley M, Howard M, Dean C (2017) Distinct phases of Polycomb silencing to hold epigenetic memory of cold in Arabidopsis. Science 10.1126/science.aan1121

This is another manuscript resulting from the extremely fruitful collaboration between the labs of Caroline Dean and Martin Howard at the John Innes Centre. This paper again focuses on the FLC locus and provides evidence for a new mechanism that defines how the binding of a subset of PRC2 factors nucleates a small region (<500bp) of chromatin at the FLC TSS, causing an increase in the repressive H3K27me2 histone mark. This metastable region serves as the seed for the development of stable epigenetic marks across the length of the locus through the activity of other distinct Polycomb factors. This occurs after a cold treatment and causes the spread of H3K27me2 repression. The novelty of this work is in the distinct temporal separation of phases of silencing, which ultimately result in the repression of FLC expression after a prolonged cold treatment.

Seki M, Ohara T, Hearn TJ, Frank A, da Silva VCH, Caldana C, Webb AAR, Satake A (2017) Adjustment of the Arabidopsis circadian oscillator by sugar signalling dictates the regulation of starch metabolism. Sci Rep. 10.1038/s41598-017-08325-y

Open Access

Research from Alex Webb’s group at the University of Cambridge features in the ARR for the second consecutive week, again on a similar topic. On this occasion they collaborate with Japanese colleagues to investigate the role of the circadian clock on determining the nighttime usage rate of starch that has accumulated during the day. They used a phase oscillator model to explain the link between the speed of the clock, starch breakdown and the maintenance of sucrose homeostasis. In addition they use Arabidopsis sugar response mutants to show that the circadian clock measures amount of cellular sucrose, which then controls the dynamics of starch breakdown.

Karpinska B, Alomrani SO, Foyer CH (2017) Inhibitor-induced oxidation of the nucleus and cytosol in Arabidopsis thaliana: implications for organelle to nucleus retrograde signalling. Philos Trans R Soc Lond B Biol Sci. 10.1098/rstb.2016.0392 Open Access

Christine Foyer (University of Leeds) is the corresponding author on this paper that looks at the effect of cellular oxidation on retrograde signaling between chloroplasts, mitochondria and the nucleus. They use a novel in vivo redox reporter to measure the effect of commonly used organelle inhibitors on cellular redox state. They discovered that these inhibitors cause a variety of effects on redox state and gene expression, which differed dependent on cell type. Researchers should be aware of these effects when they are drawing conclusions from their own experiments using these inhibitors.

Wilson DC, Kempthorne CJ, Carella P, Liscombe DK, Cameron R (2017) Age-Related Resistance in Arabidopsis thaliana Involves the MADS-domain Transcription Factor SHORT VEGETATIVE PHASE and Direct Action of Salicylic Acid on Pseudomonas syringae. Mol Plant Microbe Interact 10.1094/MPMI-07-17-0172-R

Phillip Carella is a Research Fellow at SLCU and this work from this previous lab in Canada investigates Arabidopsis Age-Related Resistance (ARR), a process that requires SA accumulation, which is then thought to act as an antimicrobial agent. The ARR response is lacking in plants containing a mutation in for the SHORT VEGETATIVE PHASE (SVP) gene. These svp plants have reduced SA, thought to be due to uncoupled overactivity of the SUPPRESSOR OF OVEREXPRESSION OF CO 1 gene. Overall this study shows that the flowering time gene SVP plays a complementary role in the control of SA accumulation, which confers ARR to older plants.

Fernie AR, Bauwe H, Sweetlove LJ (2017) Investigating the Role of the Photorespiratory Pathway in Non-photosynthetic Tissues. Methods Mol Biol 10.1007/978-1-4939-7225-8_15

Lee Sweetlove (University of Oxford) describes a protocol for evaluating the role of the photorespiration on the control of growth in non-photosynthetic tissues. This can be scaled for use in both Arabidopsis and in larger plants.

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