| Biotic stress is one of pathogenic factors, producing large yield losses and reducing grain quality by myctoxins responsible for causing human or animal disease. An effective approach to control pathogen is to breed resistant cultivars. Therefore, understand of the crosstalk of plant and pathogen will be greatly important for genetically improving the disease resistant crops.Part I:Plants and fungi utilize oxylipins for as endogenous signals. During symbiotic or parasitic interactions, oxylipins are hypothesized to be reciprocally exchanged governing inter-organismal interactions. The maize lipoxygenases (LOX) gene ZmLOX3 has been implicated previously in seed-Aspergillus interactions, so wild-type and nine oxylipin-mutant strains of Aspergillus flavus were employed to infect wild type and lipoxygenase 3 mutant (lox3) of maize to examine the effect of the mutations on fungal colonization, conidiation, mycotoxin biosynthesis, and potential association of these processes with host phytohormone content. The results showed that the presence and expression of LOX3 correlate negatively with colonization regardless of the fungal genotype indicating a general defensive role for LOX3 against A. flavus colonization. Our results provide strong evidence that the fungal LOX gene is required for normal colonization of seed, while the four other oxylipin-producing oxygenases, called Psi-producing oxygenases (Ppo) function primarily in the regulation of conidia production. PpoA was found to be required for normal aflatoxin production. The ratios of ABA and IAA to jasmonates correlate positively with increased aflatoxin accumulation. These findings are expected to expedite studies in seed-fungal interactions, lead to uncovering novel regulators of conidiation and mycotoxin production, and provide the maize industry with biochemical markers for selecting aflatoxin resistant lines.Part Ⅱ:We have previously reported that disruption of a maize root-expressed 9- lipoxygenase (9-LOX) gene, ZmLOX3, results in negatively regulates induced systemic resistance to Colletotrichum graminicola. Despite evident economic significance of these findings, the mechanism behind this negative regulator of ISR long distance signaling remained elusive. ZmLOX12 gene involved in constitutively activated ISR signaling are over-expressed in the lox3 mutant. ZmLOX12. This gene is distantly related to known dicot LOX genes, with closest homologs found exclusively in other monocot species. Disruption of a 9-LOX, LOX12, resulted not only in the complete loss of T. virens-triggered ISR but in strongly pronounced novel phenotype of T. virens-dependent Induced Systemic Susceptibility (ISS). This result suggest LOX12 are induced in roots by WT T. virens in SM1-dependent manner. Jasmonates have a strongde defense pathogen role in ISR, so reduced resistance to the pathogen is accompanied by diminished levels of the jasmonic acid (JA) precursor 12-oxo phytodienoic acid, JA-isoleucine, and expression of jasmonate-biosynthetic genes.Part III:To understand the regulatory mechanism of ZmLOX12 gene expression, we isolated and characterized the ZmLOX12 promoter (PZmloxl2)—the 5’ flanking region of ZmLOXl2. PZmLOX12 was fused to the GUS reporter gene, and was analyzed by Agrobacterium-mediated transformation into Arabidopsis. Sequence analysis showed that several cis-acting elements (BIHD10S, ASF1-motif, GCC-core and MYB-core, pollen-specific cis-acting elements POLLEN 1LELAT52) were located within the promoter. PZmLOX12 can be induced GUS expression treated by Trichoderma virens. The promoter was sufficient to improve transcription of GUS gene under hormones MeJA as well. These data further demonstrated that the expression of ZmLOXl 2 is regulated by T. virens and JA in vivo. |
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