Host-Induced Silencing of Some Important Genes Involved in Osmoregulation of Parasitic Plant Phelipanche aegyptiaca

Non-specific effect of double-stranded RNAs on Egyptian broomrape (Phelipanche aegyptiaca) seed germination

Obligate root parasitic plants of the Orobanchaceae family exhibit an intricate germination behavior. The host-dependent germination process of these parasites has prompted extensive research into effective control methods. While the effect of biomaterials such as amino acids and microRNA-encoded peptides have been explored, the effect of double-stranded RNAs (dsRNAs) has remained unexamined during the germination process. In this study, we asked whether an exogenously applied dsRNA can inhibit the germination of a root parasite, P. aegyptiaca. To this end, a dsRNA was designed to target the CYP707A1 (dsCYP7), a marker gene of the chemically-dependent germination of broomrape seeds. Application of a concentrated dsCYP7 significantly reduced seed germination. However, two non-germination-specific dsRNAs designed to target mannose-6-phosphate reductase and green fluorescent protein brought about similar inhibitions. Moreover, applying rNTPs and dNTPs, which mimic nitrogenous bases of nucleic acids, also caused a similar reduction in germination, suggesting that the non-specific inhibitory effect of the dsRNAs might arise from their nucleotides. While dsRNA application inhibited seed germination, their non-specific effects may pose a challenge for their application in studying root parasites germination. This underscores the importance of finding solutions to minimize the non-specific effects of dsRNAs to improve the potential of dsRNA as a tool to study and control root parasitic plants.

Gene silencing in broomrapes and other parasitic plants of the Orobanchaceae family: mechanisms, considerations, and future directions

Holoparasites of the Orobanchaceae family are devastating pests causing severe damage to many crop species, and are nearly impossible to control with conventional methods. During the past few decades, RNAi has been seen as a promising approach to control various crop pests. The exchange of small RNAs (sRNAs) between crops and parasitic plants has been documented, indicating potential for the development of methods to protect them via the delivery of the sRNAs to parasites, a method called host-induced gene silencing (HIGS). Here we describe various approaches used for gene silencing in plants and suggest solutions to improve the long-distance movement of the silencing triggers to increase the efficiency of HIGS in parasitic plants. We also investigate the important biological processes during the life cycle of the parasites, with a focus on broomrape species, providing several appropriate target genes that can be used, in particular, in multiplex gene silencing experiments. We also touch on how the application of nanoparticles can improve the stability and delivery of the silencing triggers, highlighting its potential for control of parasitic plants. Finally, suggestions for further research and possible directions for RNAi in parasitic plants are provided.

CRISPR gene editing to improve crop resistance to parasitic plants

Parasitic plants pose a significant threat to global agriculture, causing substantial crop losses and hampering food security. In recent years, CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) gene-editing technology has emerged as a promising tool for developing resistance against various plant pathogens. Its application in combating parasitic plants, however, remains largely unexplored. This review aims to summarise current knowledge and research gaps in utilising CRISPR to develop resistance against parasitic plants. First, we outline recent improvements in CRISPR gene editing tools, and what has been used to combat various plant pathogens. To realise the immense potential of CRISPR, a greater understanding of the genetic basis underlying parasitic plant-host interactions is critical to identify suitable target genes for modification. Therefore, we discuss the intricate interactions between parasitic plants and their hosts, highlighting essential genes and molecular mechanisms involved in defence response and multilayer resistance. These include host resistance responses directly repressing parasitic plant germination or growth and indirectly influencing parasitic plant development via manipulating environmental factors. Finally, we evaluate CRISPR-mediated effectiveness and long-term implications for host resistance and crop improvement, including inducible resistance response and tissue-specific activity. In conclusion, this review highlights the challenges and opportunities CRISPR technology provides to combat parasitic plants and provides insights for future research directions to safeguard global agricultural productivity.