Abstract
Worldwide, citrus is one of the most important fruit crops and is grown in more than 130 countries, predominantly in tropical and subtropical areas. The healthy progress of the citrus industry has been seriously affected by biotic and abiotic stresses. Several diseases, such as canker and huanglongbing, etc., rigorously affect citrus plant growth, fruit quality, and yield. Genetic engineering technologies, such as genetic transformation and genome editing, represent successful and attractive approaches for developing disease-resistant crops. These genetic engineering technologies have been widely used to develop citrus disease-resistant varieties against canker, huanglongbing, and many other fungal and viral diseases. Recently, clustered regularly interspaced short palindromic repeats (CRISPR)-based systems have made genome editing an indispensable genetic manipulation tool that has been applied to many crops, including citrus. The improved CRISPR systems, such as CRISPR/CRISPR-associated protein (Cas)9 and CRISPR/Cpf1 systems, can provide a promising new corridor for generating citrus varieties that are resistant to different pathogens. The advances in biotechnological tools and the complete genome sequence of several citrus species will undoubtedly improve the breeding for citrus disease resistance with a much greater degree of precision. Here, we attempt to summarize the recent successful progress that has been achieved in the effective application of genetic engineering and genome editing technologies to obtain citrus disease-resistant (bacterial, fungal, and virus) crops. Furthermore, we also discuss the opportunities and challenges of genetic engineering and genome editing technologies for citrus disease resistance.
Highlights
The genus Citrus and related genera (Fortunella, Poncirus, Eremocitrus, and Microcitrus), representing one of the most widely grown fruits, belong to the angiosperm subfamily Aurantioideae of the Rutaceae family [1]
Intron-hairpin RNA transcripts corresponding to citrus psorosis (CP) genes of citrus psorosis virus (CPsV) were introduced into sweet orange, leading to the regeneration of transgenic plants expressing ihpRNA with enhanced CPsV resistance [113]
Due to some of the biological characteristics of citrus, conventional breeding methods have demonstrated limitations to producing new citrus cultivars with an improved resistance to diseases
Summary
The genus Citrus and related genera (Fortunella, Poncirus, Eremocitrus, and Microcitrus), representing one of the most widely grown fruits, belong to the angiosperm subfamily Aurantioideae of the Rutaceae family [1]. Genetic manipulation has been employed as a new route to overcome the intrinsic barriers of traditional techniques, and genetic engineering methods based on the introduction of transgenes and development of transgenic plants have been successfully adopted to improve crops [14]. By introducing bioengineering technology in crop-breeding issues, genetically modified crops with an improved quality, enhanced resistance to biotic or abiotic stresses, increased yield, or reduced harmful components have been generated [15,16,17]. During the last two or three decades, genetic engineering methods based on the use of transgenes have been successfully adopted to improve fruit plants and have been mainly focused on an enhanced tolerance to biotic and abiotic stresses, increased fruit yield, improved post-harvest shelf life, reduced generation time, and production of fruit with a higher nutritional value [18]. The opportunities and challenges of genetic engineering and genome editing technology for citrus disease resistance are discussed here
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