Screening Of Insect-resistant Related Mutants And Preliminary Mapping Of Related Genes In Maize

Insect damage is one of the important factors causing the loss of maize production. One of the sufficient pest control strategy is transferring the insecticidal cry gene from bacillus thuringiensis into maize to acquire insect-resistant corns by the genetic engineering. Plant transgenic technology has opened up a new approach to crop genetic improvement. Improving the insect resistance of crop itself is also one of the effective ways of crop genetic improvement. In this study we attempt to obtain insect-resistant mutants through the screening of endogenous insect-resistant related mutants, in hope of creating beneficial conditions for crop genetic breeding and research on molecular mechanism of insect resistance in future.The EMS-mutagenized Zheng58 maize library around 33000 seeds was screened to acquire the insect-resistant mutants. The preliminary and repeated screening were operated by the mothods of standardized bioassays in laboratory and artificial infestation in the field to Asia corn borers(Ostrinia furnacalis). In the successively 3 generation screening, we finally obtained 10 insect-resistant mutants, whose leaves damage grade were less 3 according to the International Bioassay Standard. The phenotype of one mutant named M264 was further identified, which showed that a nanoid plant type, about 0.8 m height, shorter internode, bottle-green leaves, smooth leaf surface, no trichome, less stamen branch, and higher insect resistance. In the study, we obtained 24 pairs of primers, whose amplification products shared stable polymorphism, from 315 pairs of SSR primers. By the PCR amplification and PAGE analysis of the insect-resistant and dwarf 200 DNA samples from F2 population, the target gene was preliminarily located on Bin 5.05. Between umc1687 and umc2086, the genetic distance was 2.6 cM from umc1687 and 3.8 cM from umc2086, respectively.The phytohormone jasmonate plays a pivotal role in plant systemic resistance to herbivores attack as a long-distance mobile signal. To demonstrate the JA signal pathway and the insect-resistant mechanism in maize, we utilized an improved screening approach of maize mutants to screen the mutants associated with JA signal pathway, which will be available for further research. The 6118 lines’ seeds from EMS-mutagenic maize mutants library were cultivated, in the medium contained the exogenous MeJA. The different tolerance of the mutants to MeJA was identified by observing the growth of maize roots. When the final concentration of MeJA was 50 μmol L-1, 61 MeJA-insensitive mutants for tolerance Grade I were obtained in the primary screening experiment. When the final concentration of MeJA was 100 μmol L-1 or 200 μmol L-1, 37 and 10 tolerant events were gained in the confirmation experiments, respectively. Then, we analyzed the heredity of M1 seeds to tolerate MeJA. The results suggested that the tolerance of the mutants to MeJA is hereditable. We also analyzed the expression levels of several genes of key enzymes in JA pathway. The results showed that expression levels of these genes changed significantly in the mutants. The MeJA-insensitive mutants associated with JA regulation pathway and signal transduction are the potential materials for the further studies of JA signal pathway and insect resistant mechanism in maize.