Citrus Genetic Transformation: An Overview of the Current Strategies and Insights on the New Emerging Technologies

CONTI, G.; XOCONOSTLE-CÁZARES, B; MARCELINO-PÉREZ, GABRIEL; HOPP, H.E.; REYES, C.A.

Frontiers in Plant Science

Frontiers Media S.A.

Lugar: Lausanne; Año: 2021

1664-462X

Citrus are among the most prevailing fruit crops produced worldwide. Theimplementation of effective and reliable breeding programs is essential for copingwith the increasing demands of satisfactory yield and quality of the fruit as well asto deal with the negative impact of fast-spreading diseases. Conventional methodsare time-consuming and of difficult application because of inherent factors of citrusbiology, such as their prolonged juvenile period and a complex reproductive stage,sometimes presenting infertility, self-incompatibility, parthenocarpy, or polyembryony.Moreover, certain desirable traits are absent from cultivated or wild citrus genotypes.All these features are challenging for the incorporation of the desirable traits. Inthis regard, genetic engineering technologies offer a series of alternative approachesthat allow overcoming the difficulties of conventional breeding programs. This reviewgives a detailed overview of the currently used strategies for the developmentof genetically modified citrus. We describe different aspects regarding genotypevarieties used, including elite cultivars or extensively used scions and rootstocks.Furthermore, we discuss technical aspects of citrus genetic transformation proceduresvia Agrobacterium, regular physical methods, and magnetofection. Finally, we describethe selection of explants considering young and mature tissues, protoplast isolation,etc. We also address current protocols and novel approaches for improving the in vitroregeneration process, which is an important bottleneck for citrus genetic transformation.This review also explores alternative emerging transformation strategies applied tocitrus species such as transient and tissue localized transformation. New breedingtechnologies, including cisgenesis, intragenesis, and genome editing by clusteredregularly interspaced short palindromic repeats (CRISPR), are also discussed. Other relevant aspects comprising new promoters and reporter genes, marker-free systems,and strategies for induction of early flowering, are also addressed. We provided a futureperspective on the use of current and new technologies in citrus and its potential impacton regulatory processes.