The recurring pattern of “back-to-nature” movement has taken on a new meaning in the current time. While there is the usual rise in environmental awareness among populations, there is also the growing interest in using plants as sustainable industrial tools. There is no doubt that plants have played a vital role in human existence by producing oxygen and thus, it is of not much surprise that after much ignorance, we are finally looking for sustainable solutions to problems that industrialization has led to.

 

The case of treatment of malaria hopefully will shed more light to what I am trying to get at. Quinine, found in the bark of the cinchoa tree, have been used to treat malaria since the 17th century. But as we progressed technologically, the active ingredient, quinoline, was no more extracted from the plants, but rather synthesized in lab and soon after, synthetic analogues with higher potency were available in the market. But with the rise of multidrug-resistant strain of Plasmodium falciparum, the race to develop a novel anti-malarial agent led to the discovery of Artemisinin, found in the leaves of  the herb Artemisia annua in the 1970s from a Chinese medical book from the middle of the 4th century. But given our “need” for efficiency and circumstantial demand, the highly expensive process of naturally extracting it or chemically synthesizing it failed to make it a highly accessible drug in the market. With the advent of synthetic biology, we seemed to have cleared this hurdle too, when researchers found a way to produce a precursor, Amorpha-4,11-Diene in both E. coli (ref, ref) and yeast (ref). This was taken a step further when  the biotechnology company, Amyris Biotechnologies, announced that they had successfully produced a semisynthetic artemisinin precursor in yeast and were moving it to the production stage (ref).  Despite all these developments, the production of actual artemisinin was not possible in engineered microbial and plant systems till Vainstein et al (2011) reported the synthesis of Artemisinin in an engineered tobacco plants. Once cannot help but notice the recurring pattern of consistently looking into the Plant kingdom for answers that we have followed in developing anti-malarial treatments.

 

And it is not only diseases that plants are providing the answers for. Although ethanol-based biofuels have not been quite the success they had been imagined to be, it was our narrow “vision” of producing energy in liquefied form (probably stemming from our oil addiction) that led to the failure. A recent study showed  on average, converting plants that are sources of ethanol for biofuels, to bioelectricity led to 56% more energy for transportation per acre, even considering that the same biomass was also used to produce ethanol for cattle feed. When concerns were raised about CO2 emissions from production of ethanol, the researchers suggested modifying the power plant to actually capture and store CO2, resulting in a carbon-negative production process. While this is still in the works, the research for greener biofuels have led to the use of halophytes for producing the next generation of biofuels by the GreenLab at NASA. The researchers have developed an “extremely green” sustainable ecosystem for producing biofuels that do not need fresh water or fertile land that could be used for crop production. Outside the biofuel field, researchers are now looking into the process of artificial photosynthesis, the signature energy and food producing mechanism of plants till cyanobacteria came into the picture, as a sustainable renewable energy source through solar-driven generation of hydrogen (ref). The freshest step in this project comes with the development of the artificial leaf, which exhibited twice the efficiency compared to the natural photosynthetic efficiency of bacterial species, and the development of photovoltaic cells that can store solar energy like plants do, by splitting water. The research page of the Joint Center for Artificial Photosynthesis shows how this technology is inherently based the design of photosystems existing in both plants and cyanobacteria (more here).

 

Plants have also long served as indicators of changes in environmental quality resulting from anthropogenic activity (1, 2, 3, 4). Given the current decline in the environmental quality, there is an increasing need to monitor introduction of the plethora of synthetic substances that we use in our daily lives. Since these synthetic compounds usually do not have naturally occurring receptors in plants, research into fine-tuning plants to sense such foreign substances have resulted in the design of a completely synthetic detection system using periplasmic binding proteins (PBPs). These proteins, usually involved in bacterial chemotaxis, had been previously engineered to detect toxic agents. Because it is not possible to spread the engineered bacteria all around the globe, the researchers looked towards developing an easily readable system with fast detection methods. And thus, using a synthetic “de-greening” gene circuitry, where there is rapid loss of chlorophyll as response to a particular input, the engineered evolutionary conserved (between bacteria and plants) histidine kinase pathway of signal transduction and gene expression regulation, and the engineered PBPs and their receptors, the researchers effectively created a synthetic detection system that can be used for monitoring environmental contaminants. And not only as environmental indicators, but plants could be also used to study genetic variation in humans, as this recent study suggests. The analysis of 250,000 single nucleotide polymorphisms (SNPs) present in 1,307 global variants of Arabidopsis thaliana showed that the historical pattern of recombination in this plant is similar to the one observed in humans, but very different from the ones observed in other plant species.

 

On a more molecular scale, we are beginning to understand the profound impact plants have had throughout our evolution. A recent study showed that 5% of all small RNAs present in the human sera were plant microRNAs (miRNA). MicroRNAs are involved in the post-transcriptional regulation of gene expression through the RNA interference system and has entered the our bodies through the plant contents of our diets. Because they can survive the process of cooking, and given their ability to affect gene expression in our cells (eg – plant miR168, found in rice, inhibited LDLRA production, a protein involved in the removal of LDL from blood), a new alarm about genetically modified crops have been raised (ref). But as Charlie Petit of the Knight Science Journalism Tracker pointed out, the risks involved in ingesting GM plant miRNAs are not restricted only within GM crops, but are also packaged along with miRNAs from all the other food that we eat (a more detailed critique of that article can be found here). On the topic of eating, it seems that plants can also act as modes for horizontal gene transfer from bacteria to humans, as seen in Japanese populations who have received sea-weed digesting genes from the sea-dwelling bacterium Zobellia galactanivorans (ref).

 

As we frantically search for solutions to our existential crisis (literally), we are constantly looking towards the Plant kingdom for salvation where our technology has failed, essentially treating plants as Plan B. It is essential for humans to acknowledge their symbiotic relationship with plants and other components of their ecosystem for the continued survival of the species. And it looks like there is still hope.