**1. Introduction**

The development of efficient fuel and its sustainability is the major topic of concern in the time of climate change and food insecurity. The generation of efficient sources of fuel and fiber delineates the ways for the development of sustainable sources of fuel. Biodiesel is an alternative to petroleum-based fuels derived from a variety of feedstocks; including vegetable oils, animal fats, and waste cooking oil [1]. At present, biodiesel is mainly produced from conventionally grown edible oils such as soybean, rapeseed, sunflower, and palm. The cost of biodiesel is the main obstacle to commercialization of the product [2, 3]. Biodiesel produced from edible oils is

currently not economically feasible. On the other hand, extensive use of edible oils for biodiesel production may lead to food crisis. The complexity is diverse in case of food and fuel crops, and raw material is derived from plant seed oils and animal fats and is a mixture of the alkyl esters of long-chain fatty acids, mainly produced by transesterification methodology [4]. The concentration of useful fatty acid is the basis of selection, and the utility of biodiesel can be increased by focusing on the traits related to direct production of oil and its quality.

Before focusing on the mitigation practices, other ways of dissection of traits can be done to improvise the genetic architecture of crop plants. The dissection of various properties relevant to biofuel development can be targeted. The physicochemical properties of biodiesel are very similar to those of petroleum diesel and, therefore, could be used as an alternative to diesel in conventional diesel engines without the need for any modifications [5]. In contrast to conventional fuels, other advantages of biodiesel include higher cetane number, flash point, and lubricity, absence of sulfur, and lower aromatics content compared with the petroleum diesel [6, 7]. The density, viscosity, cetane number, linolenic acid, methyl ester, polyunsaturated methyl esters, acid value, glycerides content come under the major parameters of physiochemical properties and are considered before making suitable mixture with commercial diesel [8, 9]. These parameters are of prime importance to study before subjecting oilseed crops to get biofuel. The quality and content of oil are also of basic and utmost important feature to observe and determination for fatty acid profile and important physiochemical properties [10]. Currently, the majority of the commercial production of biodiesel is dependent on oils derived from palm, soybean, and rapeseed by conventional methods. Changing the direction of biodiesel production from food crops to nonedible plants requires significant improvements in oil yield and quality of these plants as well as in their tolerance to biotic and abiotic stresses. As discussed throughout the present article, biotechnological interventions and genetic engineering approaches have shown great potentials to achieve these goals [11]. However, the application of such technologies in oil plants is at their starting points, and there is no commercial oil plant with enhanced oil content or composition yet; there are laboratory and pilot-scale samples though. Moreover, it is also necessary to thoroughly evaluate the potentials of genetic engineering technology in improving several other attributes of oil plants, i.e., environment adaptation, production cost, and economic feasibility in field scale [12]. Lack of the presence of superior genotypes as a base for genetic engineering especially for nonedible plants such as *Jatropha,* which is known as one of the most important to study but not implemented and proved as one of the drawbacks in pursuing this path [13]. Developing high-throughput tissue culture and transformation protocols for oil plants is also very important to produce a large number of primary GM lines. This is very critical for especially woody perennial trees. Most of the GM oil crops have been evaluated at laboratory or greenhouse levels, and it is not clear that their responses under field conditions are yet to be looked into [14]. It should be noted that genetic engineering methods might sometimes seem technically successful but would lead to commercial failures at large-scale production [15]. Identification and characterization of major genes involved in TAG biosynthesis pathway as well as in adaptation to biotic and abiotic stresses are also of grave importance [16]. In addition, it is necessary to carry out gene pyramiding programs to collect different agronomical traits in single superior genotypes of oil plants. This would help breeders to accelerate achieving superior genotypes suitable for commercial biodiesel production. Another challenge would be the biosafety issues related to GM oil plants, necessitating performing environmental and health risk assessments for such plants before commercial release.

This would include evaluation of GM plants risks related to gene flow and potential negative effects on non-target organisms as well as the risks of potential negative effects on human and animal health.
