Plant Biology Highlights: Science Articles 2016

Plant biologists mostly put their focus on plant specific journals such as The Plant Cell, Plant Physiology, Nature Plant, The Plant Journal, Journal of Experimental Botany, Plant, Cell & Physiology, Molecular plant etc. Apart from these journals, striking findings about plant sciences are also published in Science, Nature, Cell, PNAS etc.  

This is the last month of 2016. I was going through major journals and trying to find out what I missed. Definitely I missed so many which are not directly linked to my research or study. So, I have decided to compile all plant biology related articles from major non-plant specific journals and summarize. In this post, I've summarized from Science.  

As plant roots grow through the soil, lateral roots emerge to reach more resources. In this paper, Xuan et al. showed that programmed cell death sets the course for lateral root development. Cells in a specialized region of the root cap periodically die off as a group, defining a location at which a lateral root will later develop. 

Nuclear-localized cyclic nucleotide-gated channels mediate symbiotic calcium oscillations

Plant cell nuclei respond to signals from symbiotic nitrogenfixing rhizobial bacteria or arbuscular mycorrhizal fungi with oscillating Ca2+ release. Here, Charpentier et al. identified a trio of responsible Ca2+ channels in a legume. These channels contain nuclear localization signals and are expressed in root cell nuclear envelopes. The channels function early in the establishment of symbiosis to produce oscillations in Ca2+ release from nuclear stores.

Detection of plant parasite Cuscuta reflexa by a tomato cell surface receptor  

The parasitic plant known as dodder attaches to its hosts and sucks the life out of them. Oddly, the common tomato stands tall when under attack. In this research article, Hegenauer et al. have leveraged that difference to identify part of the molecular defense system that protects tomato plants . In a process analogous to defenses mounted against microbial infection, the host plant perceives a small-peptide signal from the parasitic plant and initiates defense responses. The candidate receptor isolated from the tomato plant provided partial protection when transferred to two other susceptible plant species.

Arabidopsis transcriptional repressor VAL1 triggers polycomb silencing at FLC during vernalization 

The determinants that specify the genomic targets of Polycomb silencing complexes are still unclear. Polycomb silencing of Arabidopsis FLOWERING LOCUS C (FLC) accelerates flowering and involves a cold-dependent epigenetic switch. Here they identified a single point mutation at an intragenic nucleation site within FLC that prevents this epigenetic switch from taking place. The mutation blocks nucleation of plant homeodomain–Polycomb repressive complex 2 (PHD-PRC2) and indicates a role for the transcriptional repressor VAL1 in the silencing mechanism. VAL1 localizes to the nucleation region in vivo, promoting histone deacetylation and FLC transcriptional silencing, and interacts with components of the conserved apoptosis- and splicing-associated protein (ASAP) complex. Sequence-specific targeting of transcriptional repressors thus recruits the machinery for PHD-PRC2 nucleation and epigenetic silencing. 

Circadian regulation of sunflower heliotropism, floral orientation, and pollinator visits 

The growth of immature sunflower plants tracks the Sun's movement. The young plants lean westward as the day progresses but reorient to the east each night. As the flowers mature and open, they settle into a stable east-facing orientation. In this study, Atamian et al. showed how circadian rhythms regulate the east-west elongation of cells in the young plants' stems. They show that eastward-oriented flowers are warmer than westward-oriented flowers, and this warmth attracts pollinators. Auxin signaling pathways in the stem coordinate to fix the eastward orientation of the mature plant.

Integration of omic networks in a developmental atlas of maize 

Expression of a given gene at the RNA level does not always correlate with expression at the protein level for many organisms. Here, Walley et al. have built an integrated atlas of gene expression and regulatory networks in developing maize, using the same tissue samples to measure the transcriptome, proteome, and phosphoproteome. Coexpression networks from the transcriptome and proteome showed little overlap with each other, even though they showed enrichment of similar pathways. Integration of mRNA, protein, and phosphoprotein data sets improved the predictive power of the gene regulatory networks.

Light-dependent chlorophyll f synthase is a highly divergent paralog of PsbA of photosystem II 

Some cyanobacteria are able to use the far-red end of the light spectrum by synthesizing chlorophyll f pigments. Introducing the protein responsible for chlorophyll f synthesis into crop plants could potentially expand the range of wavelengths that such plants use during photosynthesis and thereby increase their growth efficiency. In this research article, Ho et al. identified chlorophyll f synthase (ChlF) in two cyanobacteria that are acclimatized to grow using far-red light. Introducing the ChlF-encoding gene into a model cyanobacterium allowed the organism to synthesize chlorophyll f. Similarities between ChlF and a core protein of photosystem II suggest that they have a close evolutionary relationship, and ChlF may even represent a more primitive photochemical reaction center.

Plant development regulated by cytokinin sink  

Morphogenetic signals control the patterning of multicellular organisms. Cytokinins are mobile signals that are perceived by subsets of plant cells. We found that the responses to cytokinin signaling during Arabidopsis development are constrained by the transporter PURINE PERMEASE 14 (PUP14). In our experiments, the expression of PUP14 was inversely correlated to the cytokinin signaling readout. Loss of PUP14 function allowed ectopic cytokinin signaling accompanied by aberrant morphogenesis in embryos, roots, and the shoot apical meristem. PUP14 protein localized to the plasma membrane and imported bioactive cytokinins, thus depleting apoplastic cytokinin pools and inhibiting perception by plasma membrane–localized cytokinin sensors to create a sink for active ligands. They proposed that the spatiotemporal cytokinin sink patterns established by PUP14 determine the cytokinin signaling landscape that shapes the morphogenesis of land plants.

The plant lipidome in human and environmental health 

Lipids and oils derived from plant and algal photosynthesis constitute much of human daily caloric intake and provide the basis for high-energy bioproducts, chemical feedstocks for countless applications, and even fossil fuels over geological time scales. Sustainable production of high-energy compounds from plants is essential to preserving fossil fuel sources and ensuring the well-being of future generations. As a result of progress in basic research on plant and algal lipid metabolism, in combination with advances in synthetic biology, we can now tailor plant lipids for desirable biological, physical, and chemical properties. Here, they have highlight recent advances in plant lipid translational biology and discussed untapped areas of research that might expand the application of plant lipids.

Photoactivation and inactivation of Arabidopsis cryptochrome 2 

In plants, blue light is perceived by cryptochromes, which, once activated, set off signaling events that regulate gene expression, circadian rhythms, and photomorphogenesis. In this paper,  Wang et al. showed that in the model plant Arabidopsis, one of the functions of activated cryptochromes, which are dimers or oligomers when active, is to activate production of the protein BIC1 (blue-light inhibitor of cryptochromes 1). BIC1 then favors monomerization and thus inactivation of the cryptochromes. This feedback loop resets the system so that blue-light responses can be turned off as well as turned on.

A transcriptional factor hierarchy defines an environmental stress response network 

To respond to environmental changes, such as drought, plants must regulate numerous cellular processes. Working in the model plant Arabidopsis, Song et al. profiled the binding of 21 transcription factors to chromatin and mapped the complex gene regulatory networks involved in the response to the plant hormone abscisic acid. This work has provided a framework for understanding and modulating plant responses to stress.

Increasing photosynthesis and crop productivity by accelrating recovery from photorpotection 

Crop plants protect themselves from excess sunlight by dissipating some light energy as heat, readjusting their systems when shadier conditions prevail. But the photosynthetic systems do not adapt to fluctuating light conditions as rapidly as a cloud passes overhead, resulting in suboptimal photosynthetic efficiency. Kromdijk et al. sped up the adaptation process by accelerating interconversion of violaxanthin and zeaxanthin in the xanthophyll cycle and by increasing amounts of a photosystem II subunit. Tobacco plants tested with this system showed about 15% greater plant biomass production in natural field conditions.

Phytochromes function as thermosensors in Arabidopsis 

Plants integrate a variety of environmental signals to regulate growth patterns. Legris et al.and Jung et al. analyzed how the quality of light is interpreted through ambient temperature to regulate transcription and growth. The phytochromes responsible for reading the ratio of red to far-red light were also responsive to the small shifts in temperature that occur when dusk falls or when shade from neighboring plants cools the soil.

Characterization of a dynamic metabolon producing the defense compound dhurrin in sorghum 

The specialized metabolite dhurrin breaks down into cyanide when plant cell walls have been chewed, deterring insect pests. Laursen et al. found that the enzymes that synthesize dhurrin in sorghum assemble as a metabolon in lipid membranes. The dynamic nature of metabolon assembly and disassembly provides dhurrin on an as-needed basis. Membrane-anchored cytochrome P450s cooperated with a soluble glucosyltransferase to channel intermediates toward efficient dhurrin production.

A synthetic pathway for the fixation of carbon dioxide in vitro 

Biological carbon fixation requires several enzymes to turn CO2 into biomass. Although this pathway evolved in plants, algae, and microorganisms over billions of years, many reactions and enzymes could aid in the production of desired chemical products instead of biomass. Schwander et al. constructed an optimized synthetic carbon fixation pathway in vitro by using 17 enzymes—including three engineered enzymes—from nine different organisms across all three domains of life. The pathway is up to five times more efficient than the in vivo rates of the most common natural carbon fixation pathway. Further optimization of this and other metabolic pathways by using similar approaches may lead to a host of biotechnological applications. 


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