Efficient control of root-knot nematode by expressing Bt nematicidal protein in root leucoplast.

ABSTRACT

Root-knot nematodes (RKNs) are plant pest that infect the roots of host plants. Bacillus thuringiensis (Bt) nematicidal proteins showed toxicity to nematodes. However, the application of nematicidal proteins in plant protection is hampered by the lack of effective delivery system in transgenic plants. In this study, we discovered the accumulation of leucoplasts (root plastids) in galls and RKN-induced giant cells. RKN infection caused the degradation of leucoplasts into small vesicle-like structures, and are responsible for delivering proteins to RKNs, as seen through confocal microscopy and immunoelectron microscopy. We further showed that different sized proteins from leucoplasts could be taken up by female of Meloidogyne incognita by western blot analysis. To further explore the potential applications of leucoplasts, we introduced the Bt crystal protein Cry5Ba2 into tobacco and tomato leucoplasts by fusing it with a transit peptide. The resulting transgenic plants showed significant resistance to RKNs. Intriguingly, RKN females preferentially uptake Cry5Ba2 protein when it was delivered through plastids rather than the cytosol. The decrease in progeny production was positively correlated with the delivery efficiency of the nematicidal protein. In conclusion, this study provides new insights into the feeding behavior of RKNs and their ability to ingest leucoplast proteins. Furthermore, it demonstrates the potential use of leucoplasts as an efficient delivery system for nematicidal proteins, offering a promising approach for controlling nematodes.