Map-based Cloning Of The Rice SLM1 (Spreading Lesion Mimic1) Gene And Its Function In Jasmonic Acid Biosynthesis And Insect-predator-plant Interactions

Plants and pathogens or insect herbivores have long been co-evolved. Plants have acquired a series of defense mechanisms effectively against pathogen and herbivore invasion. Hypersensitive response (HR) is an important manifestation of plant defense, similar to programmed cell death reported in animals. Lesion mimic mutants (lmm) can spontaneously form a variety of necrotic spots without biotic or abiotic stresses, the feature of cell death in lmm mutants is similar to HR cell death. Such genetic defect often results in increased resistance of plants against pathogens and insects as well. Therefore, Imm mutants have been adopted to explain cell death and defense activation signaling pathways in the plant.We studied a rice spreading lesion mimic 1(slm1) obtained from gamma-ray mutagenesis of a japonica rice variety Zhonghua 11. The slm1 mutant developed spreading lesions appearing on seedlings, extending during the whole growth period, whereas plants had normal seed setting and developed healthy seeds. Genetic analysis revealed that the slm1 phenotype is controlled by a single recessive locus. Through map-based cloning with a big mapping population, we located the SLM1 gene to a 28-kb region on chromosome 2. We found that the candidate SLM1 gene, which encodes a predicted cytochrome P450 monooxygenase or hydrogen-peroxide lyase (HPL), has a large insert in its exon, resulting in knockout mutation of the gene. Complementary test confirmed that the wild-type gene could restore slm1 phenotype. We also determined its activity as hydrogen-peroxide lyase by biochemical assay in vitro. The enzyme uses hydroperoxylinolenic acid as substrate to produce GLV in the lipin metabolism pathway. Hydroperoxylinolenic acid is also the AOS substrate to produce jasmonic acid (JA). Consistent with this, the mutant accumulated high levels of JA. This increased JA generation resulted in increased resistance to rice bacterial blight(Xanthomonas oryzae pv. Oryzae, Xoo).The plant-herbivore interaction hence the underlying biochemical defense mechanism has been a hot field of plant science and agriculture. It has been long recognized that JA play an important role in the plant-herbivore interaction, mostly from studies of the model dicot plants arabidopsis, tobacco and tomato. However, how JA is involved in defense against herbivores in the monocot model crop rice remains largely unknown. And we also lack direct genetic evidence how GLV is regulated and involved in plant-herbivore-parasite interplay. We found that the slm1 mutant accumulated higher levels of JA and TrypPI than the wild-type in response to the chewing herbivore SSB (Chilo suppressalis Walker) and consequentially increased resistance to SSB. In sharp contrast, the slm1 plants were more susceptible to the sucking insect BPH (Niaparvatalugens Stal), resulting in increased selectivity feeding, egg productivity, nymphs survival ratio of BPH on the slm1 plants, and also increased attraction of the BPH egg parasitoid, Anagrus nilaparvatae, which is mediated by GLV. While overexpression lines of SLM1 decreased or increased resistance to SSB or BPH, respectively. These results indicate for the first time that metabolism regulation of JA and GLV in rice modulate distinct resistance against chewing and sucking herbivores, and also the attraction of parasites, therefore established a practical model for studying complex niche of plant-herbivore-parasite interactions.