Is CRISPR/Cas9 a way forward to fast-track genetic improvement in commercial palms? Prospects and limits

Abstract

Commercially important palms (oil palm, coconut, and date palm) are widely grown perennial trees with tremendous commercial significance due to food, edible oil, and industrial applications. The mounting pressure on the human population further reinforces palms’ importance, as they are essential crops to meet vegetable oil needs around the globe. Various conventional breeding methods are used for the genetic improvement of palms. However, adopting new technologies is crucial to accelerate breeding and satisfy the expanding population’s demands. CRISPR/Cas9 is an efficient genome editing tool that can incorporate desired traits into the existing DNA of the plant without losing common traits. Recent progress in genome editing in oil palm, coconut and date palm are preliminarily introduced to potential readers. Furthermore, detailed information on available CRISPR-based genome editing and genetic transformation methods are summarized for researchers. We shed light on the possibilities of genome editing in palm crops, especially on the modification of fatty acid biosynthesis in oil palm. Moreover, the limitations in genome editing, including inadequate target gene screening due to genome complexities and low efficiency of genetic transformation, are also highlighted. The prospects of CRISPR/Cas9-based gene editing in commercial palms to improve sustainable production are also addressed in this review paper.

CRISPR-Cas system: revolutionizing plant breeding and gene therapy

“…Repetitive sequences with spacers downstream of CRISPR were found first in 1987, after which, CRISPR was demonstrated to play role in the immune function of bacteria and its specificity depends on the spacer sequence in 2007 [7]. The sequence's formal name, Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR), was given in 2002 [8]. In 2010 and 2011, it was reported for the first time as a programmable system for the generation of DNA cleavage at the desired site in prokaryotes [9].…”

“…Then, it was discovered that a number of small molecule substances could enhance the CRISPR-Cas9 system's function to modify genes. 8 Nowadays, CRISPR-Cas9-associated research results have been continuously published.…”

“…It should be noted the exogenous DNA sequence corresponding to the spacer sequence is the original spacer, and that the spacers formed during the acclimatisation period are highly conserved. At the end of a 5' or 3' spacer sequence, there are a number of extended base sequences, which is also preserved and called PAM (Protospacer Adjacent Motifs) [8]. PAM is considered playing an important role in the crRNA-specific recognition of target sequences.…”

“…Since this sequence stores the information of all foreign invaders, the CRISPR-Cas system will cut the sequence and it will be cut into mature crRNA by RNase III and Cas9 proteins [16]. The crRNA contains a spacer and a partial repeat sequence and forms a crRNA-tracrRNA-Cas9 complex with activity and cleavage ability under the action of endonuclease [8][16].…”

“…The transcribed spacer sequence can complement the DNA of the virus or plasmid, and the short repeat sequence fused with the spacer sequence can partially complement the tracrRNA to form RNA and RNA complexes [17]. If the spacer sequence on the cRNA matches the original spacer sequence on the exogenous invading DNA, a single Cas protein or Cas complex is activated to interfere with the exogenous DNA, causing the exogenous DNA to cleave [8].…”