Written By: Abel B. Cortinas
Written by: Ken Estrellas
Original Article: de Freitas et al. PLoS One 2019
The Gist of It
When you think about “staple foods” – items that make up a substantial portion of a given diet – rice is likely one of the first items that comes to mind. Rice is one of the most commonly consumed foods in the world, and millions of people depend upon its harvest and production to not only make a living, but also to survive. Although rice is typically grown in tropical and subtropical climates, these regions are not completely immune to unexpected drops in temperature, which could potentially damage rice plants and reduce crop yields. To gain a better understanding of how rice plants might better adapt to cold temperatures, Gabriela Moraes de Frietas and her team compared four different kinds of rice with different genetic makeups: Secano de Brazil and Cypress, which typically grow in tropical regions, and Nipponbare and M202, which typically grow in more temperate regions. Each of the plants’ biochemical and genetic response to temperature changes was measured, comparing growth at a normal temperature (28˚C) to growth at a lower “stress” temperature (10˚C). The tropical rice strains, which are adapted to grow at a higher temperature, showed significantly greater declines in rates of photosynthesis, water use efficiency, and gas exchange at 10˚C compared to the temperate plants. The tropical strains also showed increased signs of damage due to reactive oxygen species but also increased production of compounds and enzyme activity to counteract this damage. Gene expression analysis revealed that the temperate and tropical plants expressed different levels of stress-related genes in the face of cold temperatures. Overall, this study provides a look into how exactly rice strains adapt to cold temperatures and could potentially help farmers in various climates consider which strains of rice to plant in order to ensure that their plants not only survive, but thrive.
The Nitty Gritty
Rice (Oryza sativa L.) is a key staple crop worldwide, particularly in tropical and sub-tropical regions, and it is more sensitive to rapid temperature fluctuations than other cereals such as wheat or barley. Consequently, rapid decreases in temperature can severely damage rice plants, particularly by affecting photosynthetic machinery and overall photosynthetic processes leading to structural damage and reactive oxygen species (ROS) production, causing further damage. To elucidate the mechanisms by which O. sativa plants might develop resistance to the effects of cold temperatures, de Frietas et al. performed a biochemical and genetic comparison of tropical (Secano de Brazil, Cypress) and temperate (Nipponbare, M202) O. sativa japonica genotypes grown under normal temperature (28˚C) and lower “stress” temperature (10˚C). When grown at 10˚C, photosynthesis rate, water use efficiency, and stomatal conductance were significantly decreased in tropical plants, while intracellular CO2 concentrations and photoinhibition (measured by the fluorescent parameter Fv’/Fm’) were increased. The tropical strains also showed significantly lower levels of chlorophyll content and higher levels of lipid peroxidation at the lower temperature, which may indicate damage associated with the presence of ROS that accumulate under cold conditions. To counteract this damage, the Secano de Brazil and Cypress plants appear to increase their production of phenols and the activity of the enzyme superoxide dismutase; both strategies help reduce the effects of ROS damage. The temperate Nipponbare and M202 strains showed higher levels of glucose and sucrose at lower temperatures (these molecules can serve as osmoprotectants against freeze damage in plants), while levels of both sugars were decreased in the tropical strains – indicative of relative cryosensitivity. Finally, genetic analysis revealed that expression of the gene OsBURP16, which affects the composition of plant cell walls, was increased significantly in the tropical Secano de Brazil and Cypress strains when faced with cold temperatures. Additionally, expression of OsGH3-2 and Ctb-1, two other stress response genes, increased over time in the tropical strains, contrasting the expression pattern seen in the temperate strains. Overall, these biochemical and genetic changes could serve as useful biomarkers to be considered by farmers when determining the optimal strains for growth in a given climate, maximizing plant viability and crop yields.
Original Research Article: de Freitas, G.M., et al. “Cold tolerance response mechanisms revealed through comparative analysis of gene and protein expression in multiple rice genotypes.” PLoS One 14(2019): e0218019
Written By: Kaitlyn Sadtler
Original Article: Ackerman et al. eLife 2019
The Gist of It:
When our tissues heal after injury, there are several possible outcomes; one of the most common is scarring. A scar is a dense, disorganized lump of collagen that helps hold the tissue together, but it doesn’t necessarily do this in the most functional way. For example, with your skin, a scar protects you from the outside world – it seals up the cut – but you might not have any pigment or hair follicles or sweat glands there anymore, so it has lost its function. The same goes for other parts of our body. When our body heals or changes its tissue to have more disorganized collagen and non-functional tissue, we call that fibrosis. This can also happen in dysfunctions that aren’t necessarily due to trauma, like fibrosis in the lungs or liver. Since this type of healing – fibrosis – can severely limit the function of a tissue, researchers are looking at how to prevent fibrosis and promote regenerative healing. Researchers from the University of Rochester were looking at fibrosis in the context of tendon injury and repair. In the US alone there are > 15 million tendon injuries each year. When injured, much like the skin, our tendons are more likely to heal with a scar as opposed to returning to the way they were before the injury. Ackerman and colleagues investigated a specific protein called S100a4 (fun fact: this family of proteins has the “S100” name because in the 1960’s when they were discovered, they were found to be soluble in a neutral 100% saturated solution of ammonium sulfate). S100a4 had previously been studied in other sites of fibrosis including lung, heart, and the mouth. In mice that lacked 1 of the 2 S100a4 genes (called “haploinsufficiency”), there was an increase in regenerative healing responses and a decrease in fibrosis after tendon injury. Interestingly, if they completely blocked the action of the S100a4 protein with a drug, they found that though there was a decrease in fibrosis, the tissue itself was not as strong or functional. If they knocked out this protein completely early on in the healing process (within the first week), a weaker tissue formed than if they knocked it out later in the process. This suggests that the protein S100a4 does contribute to the fibrosis of a tendon after injury, but that you can’t just completely block it as a therapy. This research gives an avenue for preventing scar tissue formation in tendons and shows us that we will need to learn more about the timing of this healing process to make sure S100a4 is being blocked when it needs to be, but not blocked to a point that decreases the strength of the final healed tendon.
The Nitty Gritty:
In a mouse model of tendon injury and repair (flexor digitorum longus transection), Ackerman et al. evaluated the contribution of S100a4 to fibrotic tendon healing. An S100a4-Cre/ROSA-Ai9 system revealed a large presence of S100a4+ cells in the uninjured tendon as well as in cells surrounding the tendon after injury and during healing. In a haploinsufficient mouse model (S100a4GFP/+), there was a statistically significant increase in flexion angle and max load, as well as a decrease in gliding resistance. These functional outcomes correlated with a histologic examination showing increased collagen deposition in the tendon repair site by picrosirius red staining; there was also an increase in Col1a1 (mature collagen) gene expression with a decrease in α-SMA (myofibroblasts/fibrosis) gene expression as measured by RT-PCR. Direct treatment of bone marrow-derived macrophages with S100a4 recombinant protein did not result in a significant shift in macrophage polarization and instead created a heterogeneous phenotype between M1 and M2 gene expression, with increases in Inos, Cd64, Arg1, and Il1ra expression and decreases in Tnfa and Cd163 expression. There was no significant change in Cd86 and Cd206 expression. Treatment of tendon injury with the Receptor for Advanced Glycation Endproducts (RAGE) antagonist peptide (RAP) to block binding of S100a4 to its receptor improved gliding function and flexion angle compared to a vehicle control. Complete ablation of S100a4+ cells in ganciclovir-sensitive S100a4-TK mice resulted in mixed responses in healing with a notable decrease in tendon strength, suggesting a temporal role for S100a4 in the healing process. Inhibition of S100a4 activity (via ganciclovir treatment) at days 1–14 post-injury resulted in a weaker tendon than depletion from days 5–10 post-injury did. Furthermore, S100a4 cells appeared to transition to α-SMA+ myofibroblasts, with 65% of α-SMA+ myofibroblasts coming from the S100a4+ lineage prior to maturation. The authors note that findings regarding fibrosis and the interplay between S100a4+ and α-SMA+ cells have been shown to be different depending upon the tissue in question.
Original Research Article: Ackerman, J.E., et al. “Cell non-autonomous functions of S100a4 drive fibrotic tendon healing.” eLife 8 (2019): pii: e45342.
Written by: Rebecca Tweedell