Citrus Genetic Engineering for Disease Resistance: Past, Present and Future

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.

Heterologous Expression of CLIBASIA_03915/CLIBASIA_04250 by Tobacco Mosaic Virus Resulted in Phloem Necrosis in the Senescent Leaves of Nicotiana benthamiana

“…Meanwhile, CRISPR is a powerful weapon to combat viruses [52]. However, CRISPR is only a promising tool when the virulence mechanism of CaLas is still vague [45,53]. Based on our results and previous reports, we propose that E3 enzymes differential expressed in HLB tolerant and HLB susceptible citrus upon CaLas infection [25] may be considered as the target of CRISPR based on the possibility of CaLas interference with citrus development and disease resistance via targeting the specific proteins of the ubiquitin-proteasome system.…”

Citrus Psorosis Virus: Current Insights on a Still Poorly Understood Ophiovirus

“…Currently, genome editing ensured by clustered regularly interspaced short palindromic repeats (CRISPR)-based systems is considered as a crucial genetic manipulation tool that can be applied to numerous crops, including citrus. It is in fact established that CRISPR systems, such as CRISPR/CRISPR-associated protein (Cas)9 and CRISPR/Cpf1 systems, can provide a promising new corridor for producing citrus cultivars expressing resistant to different pathogens [ 123 ].…”

Citrus Taste Modification Potentials by Genetic Engineering

“…Several studies have reported using CRISPR/Cas9 system [76][77][78][79][80][81] or CRISPR/Cas12 system [82] as an efficient tool for genome editing in citrus. Great efforts have been focused on the improvement of citrus resistance to bacterial canker and HuangLongbing (HLB) through CRISPR/Cas system and conventional transformation strategies [83]. Interestingly, the isolation of monoembryonic early-flowering "Mini-Citrus", its sequence homology to cultivated citrus species, and its amenability to CRISPR/Cas9 precise editing render it a potent model system to study gene functions in citrus [81].…”