Progress in Genetic Engineering of Pigeonpea [Cajanus cajan (L.) Millsp.]: A Review

Abstract

Pigeonpea [Cajanus cajan (L.) Millsp.] is a major species of the family Leguminosae and an economically important source of food and fodder. It is highly valued as a rich source of proteins. Pigeonpea is widely grown in the semi-arid tropics and plays a role in the world agricultural economy as well as in alleviating hunger in the underdeveloped regions. Most of the regions where pigeonpea grows are semi-arid in nature, housing most of the impoverished population. They are also home to resource-starved farmers who are not blessed with modern agricultural and irrigational facilities. Thus, pigeonpea production and yield are constrained by several biotic (insect pests and fungal diseases) and abiotic (drought, heat, salinity and waterlogging) stresses, which cause enormous economic losses. Breeding efforts with wild-type varieties have had limited success due to low genetic base and sexual incompatibility. Thus, genetic engineering techniques such as Agrobacterium tumefaciens-mediated plant transformation and DNA bombardment are used as powerful tools to augment conventional breeding and expedite pigeonpea advancement by the introduction of agronomically beneficial traits in high-yielding varieties. Pigeonpea, being a recalcitrant subject, also faces severe hurdles in plant regeneration and transformation programs. Over the years, research has been done delineating both tissue culture-mediated regeneration as well as tissue culture-independent in planta methods to grow pigeonpea with the aim of transforming it genetically. Resistance to several fungal, viral and insect pests has been achieved through various approaches. One of the most important constraints to pigeonpea yield is infestation by the legume pod borer. Over the last decade, research has been conducted to develop transgenic pigeonpea expressing several cry genes that are resistant to the larvae of this important pest. Moreover, pigeonpea has also been used for edible vaccine production for the control of several animal diseases. Efforts have also been taken to generate marker-free insect-resistant transgenic plants. This study presents a comprehensive account of pigeonpea genetic engineering that has been undertaken in the last three decades. Future research concerns should not only focus on the use of different approaches for higher expression of transgene(s) but also provide a way forward for the safe expression of the transgene and overall improvement of the crop.