Leaf Mutant Research Articles

Identification and characterization of NARROW AND ROLLED LEAF 1, a novel gene regulating leaf morphology and plant architecture in rice

Leaf morphology is an important agronomic trait in rice breeding. We isolated three allelic mutants of NARROW AND ROLLED LEAF 1 (nrl1) which showed phenotypes of reduced leaf width and semi-rolled leaves and different degrees of dwarfism. Microscopic analysis indicated that the nrl1-1 mutant had fewer longitudinal veins and smaller adaxial bulliform cells compared with the wild-type. The NRL1 gene was mapped to the chromosome 12 and encodes the cellulose synthase-like protein D4 (OsCslD4). Sequence analyses revealed single base substitutions in the three allelic mutants. Genetic complementation and over-expression of the OsCslD4 gene confirmed the identity of NRL1. The gene was expressed in all tested organs of rice at the heading stage and expression level was higher in vigorously growing organs, such as roots, sheaths and panicles than in elsewhere. In the mutant leaves, however, the expression level was lower than that in the wild-type. We conclude that OsCslD4 encoded by NRL1 plays a critical role in leaf morphogenesis and vegetative development in rice.

Identification and Molecular Mapping of Stripe Leaf Mutant st(t) in Rice

A stripe leaf mutant, temporarily designated st(t), was discovered in the progeny of the indica restorer Jinhui 10 treated with ethyl methane sulfonate (EMS). This mutant displayed the variegated leaves at three-leaf stage, and the variegation developed the white irregular stripe from elongation to maturity. Compared with the wild type, the mutant decreased the chlorophyll content and increased the carotenoid content significantly. Transmission electronic microscope (TEM) observation of cell structures indicated that there was no difference between the wild type and the green part of the mutant, and both of them developed normal chloroplast. In the white part of st(t), cell development was abnormal including irregular stromal lamellae, aberrant thylakoids, and more osmiophilic granules. Genetic analysis suggested that the mutational character was controlled by a recessive nuclear gene. An F 2 population (1500 plants) derived from the cross between Xinong 1A and st(t) was constructed to map this gene, and simple sequence repeats (SSRs) RM19745 and RM19762 on chromosome 6 were determined as the flanking markers for St(t). The genetic distances between St(t) and the 2 markers were 0.07 cM and 0.27 cM, respectively. Based on the genomic sequence map of 9311, the physical distance of St(t) was estimated to be 345 kb. This result provides a basis for map-based cloning of St(t) gene and molecular marker-assisted breeding.

Colchicine-Induced Trait Variations in Azuki Bean (Vigna angularis)

Seeds of Jinnong 6 variety of azuki bean were soaked in 0.2% and 0.4% concentration of colchicines for 12 hours, respectively. The plant survival rates in M1 generation were 26.7% and 3.5%, and the variation rates were 1.24% and 1.59%, by which it was demonstrated that the higher the concentrations of colchicines, the lower the plant survival rate, and the greater the variation frequence.. The treatment of the 0.2% concentration of colchicines for 12h was optimal for the mutation of azuki bean, while more variation types were generated in the treatment of the 0.4% concentration. Compared with the control group, average number of seed per plant and 100-seed weight of between control and M 2 generation with colchicine treatment showed significant difference at 5% and 1% levels, respectively; 100-seed weight of M 3 generation had significant difference at 1% level. Three excellent lines with dominantly higher yield were gained. 263 mutants of leaf color, leaf shape, stem twining, more branch number, black pod, yellow-white seed, light red and deep seed color, large seed and late maturing in M 3 generation were obtained. The variations of leaf shape involved sword, small heart-shaped leaf and kidney leaves. The variations of leaf color included dark green, light green, yellowing and yellow spot. Early-maturing mutants were earlier from 10 to 15 days and late-maturing mutants were later from 7 to 10 days than the control. The traits of sprawl, yellow-white seed, higher plant mutant can be steadily inherited in M 4 . The traits of kidney leaf , small heart-shape, sword leaf mutants are mostly inherited, Some mutants of glave kidney leaf in M 3 separated sword, kidney, heart-shape leaves in M 4 .

Induced dwarf mutant in Catharanthus roseus with enhanced antibacterial activity

Evaluation of an ethyl methane sulphonate-induced dwarf mutant of Catharanthus roseus (L.) G. Don revealed that the mutant exhibited marked variation in morphometric parameters. The in vitro antibacterial activity of the aqueous and alcoholic leaf extracts of the mutant and control plants was investigated against medically important bacteria. The mutant leaf extracts showed enhanced antibacterial activity against all the tested bacteria except Bacillus subtilis.

Genetic Analysis and Gene Mapping of a Novel Rolled Leaf Mutant <I>rl12</I>(<I>t</I>) in Rice

Leaf is an important organ in photosynthesis, its moderate rolling could facilitate the improvement of plant population's structure and enhance light-use efficiency, which is significant in ideotype breeding. Recently, more attention has been paid to the identification of rice rolled leaf mutants and related gene cloning by breeders and geneticists. This paper reported a rolled leaf mutant, temporarily named rl12(t), from the restorer line Jinhui 10 treated by EMS. In the mutant, the initializing leaves did not roll, the mature leaves curled the upper 1/3 section of them and the older mature leaves rolled completely, the pigment contents increased significantly. To date, such phenotype has never been reported. One CMS line Xinong 1A with normal leaves was crossed with the rl12 (t) mutant, the F1/F2 populations were used for genetic analysis, suggesting that the mutant trait were controlled completely by one single dominant nuclear gene. rl12 (t) was finally located on the chromosome 10 between SWU-1 and SWU-2 with genetic distances of 1.5 and 0.2 cM, respectively. There has been no rolled leaf gene reported on this chromosome. Therefore, the RL12 (t) should be novel, and also the unique dominant rolled leaf gene mapped by molecular markers up to now. The results provide a basis for RL12 (t) gene cloning and functional analysis, as well as mechanism studies of rolled leaf and the application in plant-type breeding.

Genetic Analysis and Gene Mapping of a Novel Rolled-Leaf Mutant rl12(t) in Rice

Leaf is an important organ for photosynthesis. Moderate leaf rolling could facilitate structure improvement of plant population and enhance light-use efficiency, which is important in breeding for ideotype plants. A rolled leaf mutant temporarily named rl12(t), was obtained from the rice ( Oryza sativa L.) restorer line Jinhui 10 treated with ethyl methyl sulphonate (EMS). In the mutant, the newly developing leaves of the mutant did not roll, the upper 1/3 section of mature leaves was curled, and the older mature leaves were rolled completely. The pigment contents of the mutant increased significantly. The cytoplasmic male sterile (CMS) line Xinong 1A with flat leaves was crossed with the rl12(t) mutant to produce F 1 and F 2 populations. Genetic analysis indicated that the mutant was controlled by a single dominant gene. Gene rl12(t) was finally located on chromosome 10 between SWU-1 and SWU-2 with the genetic distances of 1.5 and 0.2 cM, respectively. Because no genes for rolled leaf trait have been previously located on this chromosome, RL12(t) should be a novel and unique dominant gene for rolled leaf.

SPL28encodes a clathrin‐associated adaptor protein complex 1, medium subunit μ1 (AP1M1) and is responsible for spotted leaf and early senescence in rice (Oryza sativa)

To expand our understanding of cell death in plant defense responses, we isolated a novel rice (Oryza sativa) spotted leaf mutant (spl28) that displays a lesion mimic phenotype in the absence of pathogen attack through treatment of Hwacheongbyeo (an elite Korean japonica cultivar) with N-methyl-N-nitrosourea (MNU). Early stage development of the spl28 mutant was normal. However, after flowering, spl28 mutants exhibited a significant decrease in chlorophyll content, soluble protein content, and photosystem II efficiency, and high concentrations of reactive oxygen species (ROS), phytoalexin, callose, and autofluorescent phenolic compounds that localized in or around the lesions. The spl28 mutant also exhibited significantly enhanced resistance to rice blast and bacterial blight. Using a map-based cloning approach, we determined that SPL28 encodes a clathrin-associated adaptor protein complex 1, medium subunit micro 1 (AP1M1), which is involved in the post-Golgi trafficking pathway. A green fluorescent protein (GFP) fusion protein of SPL28 (SPL28::GFP) localized to the Golgi apparatus, and expression of SPL28 complemented the membrane trafficking defect of apm1-1 Delta yeast mutants. SPL28 was ubiquitously expressed and contained a highly conserved adaptor complex medium subunit (ACMS) family domain. SPL28 appears to be involved in the regulation of vesicular trafficking, and SPL28 dysfunction causes the formation of hypersensitive response (HR)-like lesions, leading to the initiation of leaf senescence.

The ang3 mutation identified the ribosomal protein gene RPL5B with a role in cell expansion during organ growth

The role of translation in the regulation of higher plant growth and development is not well understood. Mutational analysis is a powerful tool to identify and study the function of genes related to a biological process, such as growth. Here we analyzed functionally the angusta3 (ang3) narrow leaf mutant. The AG3 gene was cloned by fine mapping combined with candidate gene sequencing and it corresponded to the ribosomal protein gene RPL5B. Based on amino acid sequence homology, promoter DNA sequence homology and in silico gene expression analysis, RPL5B was found to be putatively functionally redundant with RPL5A. The morphological analysis of ang3 mutants showed that the leaf lamina area was significantly reduced from the third rosette leaf on, mainly because of decreased width. Cellular analysis of the abaxial epidermal cell layer of the third leaf indicated that the cell number in the mutant was similar to that of the wild type, but the cell size was significantly reduced. We postulate that the reduced cell expansion in the epidermis contributes to the narrow shape of ang3 leaves. Growth was also significantly impaired in hypocotyls and primary roots, hinting at a general role for RPL5B in organ growth, unrelated to dorsiventral axis formation. Comparison of the transcriptome of the shoot apices of the mutant and the wild type revealed a limited number of differentially expressed genes, such as MYB23 and MYB5, of which the lower expression in the ang3 mutant correlated with reduced trichome density. Our data suggest that translation is an important level of control of growth and development in plants.

The ADAXIALIZED LEAF1 gene functions in leaf and embryonic pattern formation in rice

The adaxial-abaxial axis in leaf primordia is thought to be established first and is necessary for the expansion of the leaf lamina along the mediolateral axis. To understand axis information in leaf development, we isolated the adaxialized leaf1 (adl1) mutant in rice, which forms abaxially rolled leaves. adl1 leaves are covered with bulliform-like cells, which are normally distributed only on the adaxial surface. An adl1 double mutant with the adaxially snowy leaf mutant, which has albino cells that specifically appear in the abaxial mesophyll tissue, indicated that adl1 leaves show adaxialization in both epidermal and mesophyll tissues. The expression of HD-ZIPIII genes in adl1 mutant increased in mature leaves, but not in the young primordia or the SAM. This indicated that ADL1 may not be directly involved in determining initial leaf polarity, but rather is associated with the maintenance of axis information. ADL1 encodes a plant-specific calpain-like cysteine proteinase orthologous to maize DEFECTIVE KERNEL1. Furthermore, we identified intermediate and strong alleles of the adl1 mutant that generate shootless embryos and globular-arrested embryos with aleurone layer loss, respectively. We propose that ADL1 plays an important role in pattern formation of the leaf and embryo by promoting proper epidermal development.

Effects of mutation on Catharanthus roseus (L.) G.Don. plants and their inheritance

The plant Catharanthus roseus (L.) G.Don. (Apocynaceae), a perennial and self-pollinated plant, is of immense medicinal value due to antineoplastic activities of its leaf alkaloids. A mutation breeding programme was carried out to design a physiologically and chemically efficient plant type with increased production of secondary metabolites. This paper describes the morphology and inheritance of induced mutants, which were produced by physical and chemical mutagens. Induced mutagenesis with gamma rays and EMS in Catharanthus roseus produced six distinct mutants that differ in their growth habit and plant morphology. These mutants were dwarf mutants with obovate leaf (dwob), medium tall mutants with small leaf area (mtsl), nontrichomeous mutants (nt), upright oriented elliptical leaf mutants (upel), spoon shape leaf mutants (sp) and variegated leaf mutant (vg). Among them, dwob and mtsl mutants exhibited digenic recessive inheritance. The vg and upel leaf mutants were monogenic recessive and sp leaf mutant supports complementary gene action. Effect of mutation has positive response to the alkaloid content of Catharanthus but it varies in different mutants.

Flower color chimera and abnormal leaf mutants induced by 12C 6+ heavy ions in Salvia splendens Ker-Gawl.

The effect of 12C 6+ heavy ions bombardment on mutagenesis in Salvia splendens Ker-Gawl. was studied. Dose–response studies indicated that there was a peak of malformation frequency of S. splendens at 200 Gy. Abnormal leaf mutants of the bileaf, trileaf and tetraleaf conglutination were selected. Meanwhile, a bicolor flower chimera with dark red and fresh red flower was isolated in M1 generation of S. splendens. Random amplified polymorphic DNA (RAPD) analysis demonstrated that DNA variations existed among the wild-type, fresh and dark red flower shoots of the chimera. The dark red flower shoots of the chimera were conserved and cultivated at a large-scale through micropropagation. MS supplemented with 2.0 mg/L BA and 0.3 mg/L NAA was the optimal medium in which the maximum proliferation ratio (5.2-fold) and rooting rate (88%) were achieved after 6 weeks. Our findings provide an important method to improve the ornamental quality of S. splendens.

Plant Cells Without Detectable Plastids are Generated in the crumpled leaf Mutant of Arabidopsis thaliana

Plastids are maintained in cells by proliferating prior to cell division and being partitioned to each daughter cell during cell division. It is unclear, however, whether cells without plastids are generated when plastid division is suppressed. The crumpled leaf (crl) mutant of Arabidopsis thaliana is a plastid division mutant that displays severe abnormalities in plastid division and plant development. We show that the crl mutant contains cells lacking detectable plastids; this situation probably results from an unequal partitioning of plastids to each daughter cell. Our results suggest that crl has a partial defect in plastid expansion, which is suggested to be important in the partitioning of plastids to daughter cells when plastid division is suppressed. The absence of cells without detectable plastids in the accumulation and replication of chloroplasts 6 (arc6) mutant, another plastid division mutant of A. thaliana having no significant defects in plant morphology, suggests that the generation of cells without detectable plastids is one of the causes of the developmental abnormalities seen in crl plants. We also demonstrate that plastids with trace or undetectable amounts of chlorophyll are generated from enlarged plastids by a non-binary fission mode of plastid replication in both crl and arc6.

Genetic analysis and gene mapping of a narrow leaf mutant in rice (Oryza sativa L.)

A narrow leaf mutant was obtained after T-DNA transformation conducted on a rice variety Zhonghua 11. Several abnormal morphological characteristics, including semi-dwarf, delayed flowering time, narrow and inward rolling leaves, and lower seed-setting, were observed. The rate of net photosynthesis (under saturate light) of flag leaves in the mutant was significantly lower than that of the wild type. Moreover, the leaf transpiration rate and stomatal conductance in the mutant flag leaf were lower than those of the wild type at the grain filling stage. It was found that the mutant phenotype was not caused by the T-DNA insertion. Genetic analysis showed that the mutant was controlled by a single recessive gene, designated as nal3(t). A genetic linkage map was constructed using a large F2 mapping population derived from a cross between nal3(t) and an indica variety Longtefu B with 6 polymorphic markers on chromosome 12 identified from 366 SSR markers by the BAS method. Gene nal3(t) was mapped between the markers RM7018 and RM3331. Fine mapping of nal3(t) locus was conducted with 22 newly developed STS markers based on the sequence diversity around the region harboring nal3(t) between Nipponbare and 93–11, and nal3(t) was finally mapped to a 136-kb region between the STS markers NS10 and RH12-8.

Lessons from a search for leaf mutants in Arabidopsis thaliana

Large-scale exploratory approaches to understanding gene function laid the foundations for the -omics era. Based on modern technologies for the structural and functional characterization of genomes, these curiosity-driven approaches allow systematic accumulation of vast amounts of data, enabling subsequent hypothesis-driven research. Some years before the dawn of genomics, exploratory approaches were already furthering our understanding of gene function in the form of saturation mutagenesis experiments aimed at the identification of all genes that mutate to a given phenotype. Forward genetic approaches, conducted on experimental organisms such as Drosophila melanogaster and Caenorhabditis elegans, have led to the isolation of mutants affected in specific developmental processes, whose cellular and molecular characterization has unraveled the underlying genetic mechanisms of animal development. To shed light on the making of plant leaves, in 1993 we initiated an attempt to identify as many viable and fertile mutants with abnormal leaf morphology as possible, using the Arabidopsis thaliana model organism. We identified 25 fast-neutron- and 153 ethyl-methane sulfonate-induced mutations, which fell into eight and 94 complementation groups, respectively. We also studied 115 publicly available mutant lines isolated by previous authors, which fell into 37 complementation groups. Although we did not reach saturation of the Arabidopsis thaliana genome, the broad spectrum of leaf morphological alterations identified is facilitating the dissection of specific leaf developmental processes. In a complementary approach, we also analyzed leaf architecture in natural accessions and two populations of recombinant inbred lines. Using a high-throughput gene mapping method, we have already cloned 25 of the genes identified by mutation, in some cases in collaboration with other groups. The products of these genes participate in various developmental processes, such as polar cell expansion, transduction of hormonal signals, gene regulation, plastid biogenesis, and chromatin remodeling, among others. The range of phenotypes and processes identified reveal the complexity of leaf ontogeny and will help explain the diversity of leaf morphology in nature.

Leaf development: time to turn over a new leaf?

Molecular cloning of mutations affecting the morphology of plant leaves has proven to be useful for the causal analysis of leaf development. Studies of leaf mutants have produced a wealth of biologically meaningful information on the genes that participate in leaf initiation, leaf polarity specification and maintenance, and leaf expansion and maturation. The availability of collections of gene-indexed insertional mutants, automated platforms for high-throughput imaging, and new morphometry software is making genome-wide leaf phenomics possible and complements classical forward genetics approaches. Large-scale phenomic studies will further our understanding, among others, of two intriguing phenomena that recently reentered the leaf scenario. One is the unexpected relationship between translation and leaf dorsoventrality, recently confirmed by the severe abaxialization of double mutants involving loss-of-function alleles of the developmental selector genes AS1 and AS2 and some genes encoding ribosomal proteins. The second unexplained phenomenon is the compensatory cell enlargement experienced by some leaf mutants, in which a reduced cell number is compensated by their increased cell size compared with the wild type. This compensation suggests that cell cycling and cell enlargement are integrated in leaf primordia via cell-to-cell communication.

Expression and characterization of rice putativePAUSEDgene

In Arabidopsis, PAUSED (PSD) encodes the ortholog of los1p/exportin-t, which mediates the nuclear export of transfer RNA (tRNA) in yeast and mammals. However, in monocot plants such as rice, knowledge of the corresponding ortholog is limited, and its effects on growth development and productivity remain unknown. In this study, we verified a rice transfer-DNA insertional mutant psd line and analyzed its phenotypes; the mutant displayed severe morphological defects including retarded development and low fertility compared with wild-type rice. Examining intronless tRNA-Tyr and intron-containing pre-tRNA-Ala expression levels in cytoplasmic and nuclear fraction with Northern blot analysis between wild-type and mutant leaf tissue suggested that rice PSD might be involved in tRNA export from the nucleus to the cytoplasm. Additionally, reverse transcription-polymerase chain reaction analysis revealed that PSD transcript was expressed throughout normal rice plant development, and subcellular localization assays showed that rice PSD protein was present in both the nucleus and cytoplasm. In summary, our data implied that the putative PSD gene might be indispensable for normal rice development and its function might be the same as that of Arabidopsis PSD.

Anatomical and Chemical Characteristics of a Rolling Leaf Mutant of Rice and Its Ecophysiological Properties

The anatomical and chemical characteristics of a rolling leaf mutant ( rlm) of rice ( Oryza sativa L.) and its ecophysiological properties in photosynthesis and apoplastic transport were investigated. Compared with the wild type (WT), the areas of whole vascular bundles and xylem as well as the ratios of xylem area/whole vascular bundles area and xylem area/phloem area were higher in rlm, whereas the area and the width of foliar bulliform cell were lower. The Fourier transform infrared (FTIR) microspectroscopy spectra of foliar cell walls differed greatly between rlm and WT. The rlm exhibited lower protein and polysaccharide contents of foliar cell walls. An obvious reduction of pectin content was also found in rlm by biochemical measurements. Moreover, the rate of photosynthesis was depressed while the conductance of stoma and the intercellular CO 2 concentration were enhanced in rlm. The PTS fluorescence, which represents the ability of apoplastic transport, was 11% higher in rlm than in WT. These results suggest that the changes in anatomical and chemical characteristics of foliar vascular bundles, such as the reduction of proteins, pectins, and other polysaccharides of foliar cell walls, participate in the leaf rolling mutation, and consequently lead to the reduced photosynthetic dynamics and apoplastic transport ability in the mutant.

Arabidopsis thaliana leaves with altered chloroplast numbers and chloroplast movement exhibit impaired adjustments to both low and high light

The effects of chloroplast number and size on the capacity for blue light-dependent chloroplast movement, the ability to increase light absorption under low light, and the susceptibility to photoinhibition were investigated in Arabidopsis thaliana. Leaves of wild-type and chloroplast number mutants with mean chloroplast numbers ranging from 120 to two per mesophyll cell were analysed. Chloroplast movement was monitored as changes in light transmission through the leaves. Light transmission was used as an indicator of the ability of leaves to optimize light absorption. The ability of leaves to deal with 3 h of high light stress at 10 °C and their capacity to recover in low light was determined by measuring photochemical efficiencies of PSII using chlorophyll a fluorescence. Chloroplast movement was comparable in leaves ranging in chloroplast numbers from 120 to 30 per mesophyll cell: the final light transmission levels after exposure to 0.1 (accumulation response) and 100 μmol photons m−2 s−1 (avoidance response) were indistinguishable, the chloroplasts responded quickly to small increases in light intensity and the kinetics of movement were similar. However, when chloroplast numbers per mesophyll cell decreased to 18 or below, the accumulation response was significantly reduced. The avoidance response was only impaired in mutants with nine or fewer chloroplasts, both in terms of final transmission levels and the speed of movement. Only mutants lacking both blue light receptors (phot1/phot2) or those with drastically reduced chloroplast numbers and severely impacted avoidance responses showed a reduced ability to recover from high light stress.

Hydrophilic interaction chromatography/electrospray mass spectrometry analysis of carbohydrate‐related metabolites from Arabidopsis thaliana leaf tissue

This work describes the development and application of an on-line liquid chromatography/mass spectrometry (LC/MS) method using hydrophilic interaction chromatography (HILIC) coupled to negative ion mode electrospray ionisation ion trap mass spectrometry (ESI-MS) for the analysis of highly polar carbohydrate-related metabolites commonly found in plants, ranging from reducing and non-reducing sugars and sugar alcohols to sugar phosphates. Using this method, separation and detection of a mixture of eight authentic standard compounds containing glucose (Glc), sucrose (Suc), raffinose, verbascose, mannitol, maltitol, glucose-6-phosphate (Glc6P) and trehalose-6-phosphate (Tre6P) were achieved in less than 15 min. The method is rapid, robust, selective, and sensitive, with limits of detection (LODs) ranging from 0.2 microM obtained for neutral sugars, to 1.0 microM obtained for sugar alcohols, and 2.0 microM obtained for negatively charged sugar phosphates. We have studied the negative ion collision-induced dissociation (CID) fragmentation behaviour of the non-reducing raffinose family oligosaccharides (RFOs) raffinose, stachyose, and verbascose. Mainly Bi and Ci glycosidic and Ai cross-ring structurally informative cleavages are observed. We have applied this HILIC/ESI-MS method for the analysis of Arabidopsis thaliana wild-type Columbia-0 (Col-0) and its starchless phosphoglucomutase mutant (pgm1) leaf extracts. The method was used to quantify Glc, Suc, raffinose, and Glc6P in A. thaliana extracts. Data obtained using this HILIC/ESI-MS method were compared with those obtained using a comparable porous graphitic carbon-based LC/ESI-MS method.

Rice lesion mimic mutants with enhanced resistance to diseases

Lesion mimic mutants are characterized by the formation of necrotic lesions in the absence of pathogens. Such genetic defects often result in enhanced resistance to pathogen infection and constitutive expression of defense response genes. To understand the genetic mechanisms leading to these mutations, we characterized 21 lesion mimic mutants isolated from IR64 rice mutant populations produced by mutagenesis with diepoxybutane (D), gamma rays (G), and fast neutrons (F). Four mutations are controlled by single dominant genes, one of which is inherited maternally. Five lesion mimics are allelic to known spotted leaf (spl) mutants spl1, spl2, spl3, or spl6. In total, 11 new lesion mimic mutations, named spl16, spl17, and spl19 through Spl27, were established based on allelism tests. Two lesion mimics, spl17 and Spl26 showed enhanced resistance to multiple strains of Magnaporthe oryzae, the rice blast pathogen, and Xanthomonas oryzae pv. oryzae, the bacterial blight (BB) pathogen. Co-segregation analyses of blast and BB resistance and lesion mimic phenotypes in segregating populations of spl17 and Spl26 indicate that enhanced resistance to the two diseases is conferred by mutations in the lesion mimic genes. A double mutant produced from two independent lesion mimics showed more severe lesions and higher level of resistance to X. o. pv. oryzae than their single mutant parents indicating a synergistic effect of the two mutations. In mutants that exhibit enhanced disease resistance to both pathogens, increases in expression of defense response genes PR-10a, POX22.3, and PO-C1 were correlated with lesion mimic development and enhancement of resistance. These lesion mimic mutants may provide essential materials for a comprehensive dissection of the disease resistance pathways in rice.