Abstract
Lepidopteran insect pests are the main class of pests causing significant damage to crop plant yields. Insecticidal scorpion peptides exhibit toxicity specific for insects. Here, we report that a peptide LMX, optimized from the insect-specific scorpion neurotoxin LqhIT2, showed high levels of activity against rice leaf folder in vitro and in planta. Oral ingestion of LMX protein led to a significant decrease in feeding on rice leaves, repression of larval growth and development, delay in molting, and increase in larval lethality. Compared with LqhIT2 protein, the stability and insecticidal efficacy of LMX was better. Meanwhile, biochemical analysis showed that LMX protein ingestion dramatically decreased ecdysone content in rice leaf folder larvae, and down-regulated enzymatic activities of the detoxification system (α-naphthyl acetate esterase and glutathione S-transferase), the digestive system (tryptase and chymotrypsin), and the antioxidant system (catalase). These changes were tightly correlated with the dosage of LMX protein. Transgene analysis showed that the rate of leaf damage, and the number of damaged tillers and leaves in the transgenic line were greatly reduced relative to wild type plants and empty vector plants. Based on these observations, we propose that the insect-specific scorpion neurotoxin peptide LMX is an attractive and effective alternative molecule for the protection of rice from rice leaf folder.
Highlights
Rice (Oryza sativa) acts as a staple food for much of the global population [1], in Asia where about 90% of people live on rice [2]
After optimizing the nucleotide sequence of LMX based on rice codon preference, we introduced the gene into rice to improve resistance to rice leaf folder
Molecular optimization of LMX polypeptide In order to enhance the insecticide efficacy of LqhIT2, we changed the amino acid in the non-conservative regions of LqhIT2 to construct the optimized peptide named LMX
Summary
Rice (Oryza sativa) acts as a staple food for much of the global population [1], in Asia where about 90% of people live on rice [2]. In commercial production, rice productivity and quality are adversely affected by many biotic stresses, insect pests. Rice leaf folder (Cnaphalocrocis medinalis Guenee) is a migratory insect which causes significant damage to rice yields [3]. Rice leaf folder larvae damage rice crops by folding leaf blades and feeding inside the rolled leaves. A single larva can damage a number of rice leaves, disturbing photosynthesis and reducing the rice yield [4]. Rice leaf folder is widely distributed around the rice-growing areas of the world. In China, since 2003, the annual average area damaged by rice leaf folder was more than 20 million hm and the grain yield loss was up to 760 million kg every year. In 2011, rice leaf folder damaged 22 million hm of rice in China [5]
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