Phenotypic Characterization And Gene Function Analysis Of A Lesion Mimic Mutant Spl30 In Rice

Leaf color mutants usually reduce photosynthetic efficiency and crop yield, and even lead to plant death, thus it used to be considered useless mutants. In recent years, the value of leaf color mutants is receiving more and more attention. In the breeding, leaf color mutation can be used as a marker to simplify the breeding and hybrid seed production. Some leaf color mutants with excellent properties are provided as good germplasm resources for crop genetic breeding. In basic research, the leaf color mutants are ideal materials for the study of plant photosynthesis, morphogenesis, physiological hormone, resistant mechanism and a series of physiological and biochemical metabolism. We can also use the mutant to analyze and identify the gene function and understand the interaction of genes.Plant lesion mimic mutants, which spontaneously produced lesions that resemble disease symptoms in the absence of pathogen attack and other damages or stress conditions, were called lesion resembling disease. 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.spl30 is a lesion mimic mutant derived from 9311 by radiation. Lesions are initiated from the tip of older leaves, and then spread to the whole leaf. The content of chlorophyll, plant height, seed setting rate and seed size of spl30 are reduced compared with 9311. Transmission electron microscopy (TEM) analysis of the wild-type and non-spotted and spotted leaf sections of the mutant indicated a clear cellular difference among the samples. Chloroplasts in spotted leaf sections evidenced an abnormal shape and damaged or broken lamella, while in non-spotted leaf sections, the mesophyll chloroplasts were phenotypically normal as the wild-type. DAB staining of spl30 leaf showed that H2O2 accumulated before the appearanc of spots, suggesting that the lesions of spl30 leaves may caused by ROS.The high MAD concentration also showed an increased lipid peroxidation degree in spl30. Since the net photosynthetic rate was significantly decreased, we deduced that there were destructive effects on photosynthesis in spl30.Genomic sequence analysis revealed that only the 3th exon of LOC_Os07g0658400 carries a single-nucleotide transition (G?A). Comparison of the genomic and cDNA sequences revealed that the single-nucleotide substitution in the spl30 mutant genome created a new splicing site. The major physiological role of Fd-GOGAT was suggested to be re-assimilation of the ammonium liberated in photorespiration. Phylogenetic analysis indicated that Fd-GOGAT in rice is most closely related to the maize and Sorghum bicolor Fd-GOGAT proteins. Fd-GOGAT RNAi plants shows similar lesions as spl30, thus we confirmed that LOC_Os07g0658400 indeed corresponds to the Fd-GOGAT gene. Fd-GOGAT expression is constitutive in most tissues and most abundant in younger leaves. In addition, Fd-GOGAT protein located in chloroplast of rice protoplasts. Together, our data provide new insights into the function and regulation of Fd-GOGAT in higher plants.