Identification And Genetic Mapping Of A Lesion Mimic Stripe Mutant In Rice

Plants can exhibit spontaneous spots on leaves in the absence of environmental stresses, agrochemical damage, physical damage, and pathogen attack. This kind of spots is similar to lesions which caused by the infection of pathogen. People term this kind of mutants as lesion mimic mutant. By studying these mutants, it can play an important role in the understanding of plant cell development and apoptosis related genes and stress tolerance of plant disease resistance and other aspects of defense genes from signaling pathways. In this paper, a rice mutant lms1(lesion mimic striped mutant1) was selected from a japonica variety jiahua No.1, treated byγ-radiation. The preliminary examination of morphological character, the genetic analysis and the molecular mapping were conducted to the mutant, which lays the foundation for cloning, functional analysis and application of the gene. The main conclusions are as follows:1. The lms1 mutant growing in a glasshouse exhibited brown-yellow stripes before the first true leaf unfolding at the seedling stage. With the leaf unfolding, the stripes enlarged and grew into yellow-white streaks, where the necrotic lesion located. A leaf generally displayed two or three lesion mimics, which mostly located on the upper and middle parts of leaves. The lesion mimics were also observed on stems during the whole growth period as well as leaves. The mature mutant planted in the fields at Hainan exhibited phenotypes of dwarfed, premature senility and declining seed set percentage as compared with the wild type. The investigations of agronomic characters showed that the plant weight, the ear length, the spike number and the thousand seed weight of lms1 mutant were significant lower than the wild type.2. The phenotype of lms1 is affected by temperature. The lms1 mutant emerged white stripes on leaves under 30°C, while both white stripes and brown necrotic lesions appeared on lms1 mutant leaves at 20°C, which suggested that low temperature can accelerate the formation of lesion mimics in lms1.3. The ultrastructural analysis of leaf chloroplasts of lms1 seedlings showed that the chloroplasts from the white-stripe part of lms1 leaves were aberrant. The thylakoid discs were loose among themselves and assembled into abnormal grana, which slackly connected by stroma thylakoids. These results indicated that the mutation of lms1 influenced the development of chloroplasts.4. The chlorophyll content in the mutant was much lower than the wild type.The trypan blue staining experiment showed that the formation and development of lms1 lesion mimics might be actually the process of PCD in leaves.The DAB(diamino benzidine) staining experiment showed that the leaves from lms1 appeared a great deal of rufous spots in contrast with that of wild type. It suggested that lms1 bred the burst of reactive oxygen species (ROS) which led to hypersensitive response.5. The genetic analysis suggested that the lesion-mimic phenotype of lms1 was controlled by a single locus recessive nuclear gene. We primarily delimited lms1 on the distal end of the short arm of chromosome 6 by using F2 mapping population derived from a cross between lms1 and 9311(a typical indica variety).Than we fine-maped lms1 in a 400kb region by using another F2 mapping population derived from a cross between lms1 and Pei'ai 64S (an indica-like variety with maternal origin of japonica) and new developed marks. Through bioinformatics analysis,we concluded that the lms1 may be a new mutation gene involved with lesion mimics.