With rapidly depleting fossil fuels, alternative sources of power are acutely needed for the world's energy demands. Decades of research around the world have highlighted various plants as a source of biofuels. Edible oil sources like soybean, sunflower, and rapeseeds are used as sources of biodiesel due to their easy availability in Europe and the US. But in developing nations with large populations like India, China, and Indonesia, food security is more of a concern than an alternative fuel source. So, the research communities started exploring non-edible crops that could be grown easily.
A tropical plant, Jatropha curcas also called jangli arandi in Hindi, was identified as a potential source of biodiesel production. There is a vast scope in India for producing biodiesel from Jatropha, as it grows in plenty in wastelands or barren lands, as a fence to act as a windbreaker, to safeguard fields from livestock, and to check soil erosion during rainfall.
Biodiesel is an effective replacement for diesel fuel as it contains much fewer pollutants than diesel and might give an almost equivalent performance to diesel engines How et al. 2012. In Asia, Singapore, Indonesia, Malaysia, and China biodiesel production from Jatropha is quickly rising.
The national biodiesel mission was developed by the government of India in 2009, identifying Jatropha as a promising source for biodiesel. The pilot program for the extraction of fuel started in 2014. The popularity of this plant as a source of alternative eco-friendly fuel is evident from the fact that in 2018 the Indian Air Force (IAF) flew its first AN-32 on biofuel from Jatropha seed oil blend with aviation turbine fuel (ATF) Press release by the Ministry of Defence Dec 2018
However, the mission soon saw its downfall due to inadequate opportunities in the fuel market, sparse government incentives, lack of clear regulations, available fertile land areas, and inadequate technologies for proper processing and collection of seeds. The poor agronomic performance of Jatropha seeds was the most crucial obstacle to biodiesel production from the Jatropha plant. Large-scale cultivation of Jatropha is economically difficult as the crop usually takes 3–5 years for bearing seeds resulting in a longer payback period and creating additional problems for farmers. Constraints like high maintenance cost along with major diseases like collar rot, leaf spots, seedling blight, stem rot, anthracnose, fruit rot, and viral infestations decrease the yield drastically. The leaf curl mosaic disease caused by geminivirus is a severe threat to Jatropha and leads to high (up to 80%) yield loss. For large-scale production, it is firstly required to overcome viral disease infestation.
The conventional breeding approach for developing the geminivirus resistant varieties is not possible as the resistant gene(s) against geminivirus have not been identified in the Jatropha plant gene pool. Therefore, the biotechnological approach is the best way to develop the resistance against Gemini viruses of Jatropha.
One such study (More et al 2021) utilized the knowledge of plant defense artillery- RNA mediated gene silencing against invading viruses. The plants, like us humans, have a defense system against pathogens. They have an “RNA silencing machinery” as the first line of defense against invading pathogens including viruses. Plants produce small RNAs (miRNA) which bind to the target viral RNA, and then this dsRNA complex is cleaved by a plant protein- DCL1 (Dicer-like proteins) to inactivate the viral RNA. However, the Gemini viruses have a unique “RNA silencing suppressor” (RSS) activity as a counter-defense, and hence they successfully infect the plant (Figure 1).
To inactivate those viral genes responsible for RSS activity, artificial miRNAs are designed in vitro and transferred into plants. These artificial miRNAs act in the same way as miRNAs to inactivate the target gene (Figure 2). Interestingly, the artificial miRNA designed in this experiment also shared similarities with the target genes of other Gemini viruses, attacking economically important crops such as tomato, papaya, and pepper. Therefore, the designed artificial miRNAs have a broad target range and can be effectively used in other crops also.
In general, when a crop is infected with a virus, farmers use one or more combinations of the following steps - crop rotation, using virus-free seeds and rhizomes for propagation, elimination of virus-infected plants, controlling insect vectors, and using disease-resistant varieties. These methods are either too labor-intensive or highly expensive and also do not lead to 100% eradication of the virus. This approach using genetic engineering is effective and will certainly decline the yield loss of not only Jatropha but other important crops also.
This work was created as part of a science communication internship at BioXspace.
Edited and approved by- Dr. Jyoti Chhibber-Goel and Dr. Bharti Singal