Description

Background

Corn is an important food crop and feed crop, with large production potential and high economic benefits. It has edible, feeding and various industrial uses, and plays an important strategic position in ensuring food security. Maize, native to Central and South America, is now widely distributed in the United States, China, Brazil and Argentina, and has a history of more than 400 years in China. According to the US Department of Agriculture, China’s corn production will account for 23.02% in 2020, ranking second in the world. China is also one of the world’s largest corn consumers, with consumption reaching 289 million tons in 2020.

Overview

Among the three major grains, corn is widely distributed and has high yield, which is an important crop for food, economy and feed. In recent years, the sown area and yield of maize in China have shown an increasing trend year by year. However, due to the frequent occurrence and prevalence of pests and diseases, the yield and quality of corn are seriously damaged. Corn sheath wilt is one of the diseases on corn, which can occur all over the world. It is a fungal disease caused by Rhizoctonia solani. In recent years, due to the dense planting of corn, continuous cropping in main corn producing areas for many years and the lack of application of high-quality and high-resistance corn varieties, the incidence of corn sheath blight has accelerated, with the incidence reaching 40% in general years and 100% in severe cases, resulting in a rapid decline in corn yield and quality [1].

Sheath Blight of Maize and its control status

Maize sheath blight can occur at any stage of maize growth, from the seedling to the late growth. It mainly affects the leaf sheaths, leaves, bracts, and stems of maize, potentially causing severe ear damage.The pathogen initially infects 1-2 stem nodes and leaf sheaths near the ground, gradually spreading upwards. The lesions initially appear water-soaked and often take on an irregular or elliptical shape. As the disease advances, these lesions can expand, merging to create irregular, moiré-like patterns, ultimately leading to the withering of leaf sheaths and leaves. When the air humidity and the temperature are high, the disease exhibits dense white mycelium growth. Over time, the mycelium gradually changes color and forms a sclerotic of different sizes[3]. Crucially, the hyphae within these sclerotia can survive through the winter and serve as the primary infection source in the following year [4].

At present, the main prevention and control measures for maize blight include selection of resistant maize varieties, regular removal of weeds in the field, spraying fungicides and using microorganisms. However, these measures have some disadvantages. For example, the sclerotium left in the field to overwinter is an important source of the initial infection of the disease, and the removal of sclerotium by fishing is time-consuming and laborious. It is easy to produce drug resistance through spraying pesticide control. Therefore, new prevention and control measures need to be sought.

RNA interefence

RNA interference (RNAi) is a gene expression regulation mechanism that is conserved in eukaryotes such as plants, animals, fungi and nematodes. Inhibition of target gene expression mainly through nucleic acid sequence-specific interactions is an important defense mechanism for eukaryotes to prevent virus infection, prevent foreign nucleic acid invasion such as transposons, and regulate gene expression. In recent years, it has become possible to control plant diseases, insect pests and fungal diseases through RNAi inhibition of functional gene expression [5-6], which also opens up a new way for the prevention and control of postharvest fungal diseases of fruits and vegetables.

In recent years, pest control strategies based on RNAi mechanism have developed rapidly, and RNA molecular preparations for pest control are called nucleic acid pesticides. Compared with traditional small molecule pesticides, nucleic acid pesticides have strong target specificity, no residue, and far lower development cost than chemical pesticides, which meets the requirements of today’s society for environmentally friendly pesticides [7]. Exogenous sprayed dsRNA can be absorbed by plant leaf cells and cut into dsRNA in plants, and then transported transboundary to pathogen objects to induce silencing or directly absorbed by host surface fungi [8].

Our goal

Based on the above background, it is hoped that the expression of dsRNA targeting CAT gene of Rhizoctonia solani in E. coli HT115 can be sprayed on corn leaves, thereby reducing the infection of Rhizoctonia solani on corn, and providing a new idea for the large-scale production and application of dsRNA fungicide in the future.

Reference

[1] Wang ZY, Wang XM. Current situation, trend and control measures of maize pests and diseases in China. Plant Protection, 2019,45 (1) : 1-11.

[2] Akber MA, Mubeen M, Sohail MA, Khan SW, Solanki MK, Khalid R, Abbas A, Divvela PK, Zhou L. Global distribution, traditional and modern detection, diagnostic, and management approaches of Rhizoctonia solani associated with legume crops. Front Microbiol. 2023 Feb 6;13:1091288.

[3] Tang HT, Rong YZ, Yang JP. Research progress on corn sheath blight. Maize Sci. 2004, 12, 93-96.

[4] Georgiou CD, Patsoukis N, Papapostolou I, Zervoudakis G. Sclerotial metamorphosis in filamentous fungi is induced by oxidative stress. Integr Comp Biol. 2006 Dec;46(6):691-712.

[5] Kim J, Badaloni A, Willert T, Zimber-Strobl U, Kühn R, Wurst W, Kieslinger M. An RNAi-based approach to down-regulate a gene family in vivo. PLoS One. 2013 Nov 12;8(11):e80312.

[6] Takahashi Y, Nishikawa M, Takakura Y. Nonviral vector-mediated RNA interference: its gene silencing characteristics and important factors to achieve RNAi-based gene therapy. Adv Drug Deliv Rev. 2009 Jul 25;61(9):760-6.

[7] de Andrade EC, Hunter WB. RNA Interference - Natural Gene-Based Technology for Highly Specific Pest Control (HiSPeC) [Internet]. RNA Interference. InTech; 2016.

[8] Song XS, Gu KX, Duan XX, Xiao XM, Hou YP, Duan YB, Wang JX, Yu N, Zhou MG. Secondary amplification of siRNA machinery limits the application of spray-induced gene silencing. Mol Plant Pathol. 2018 Dec;19(12):2543-2560.