Rice Lesion Mimic Mutants (LMM): The Current Understanding of Genetic Mutations in the Failure of ROS Scavenging during Lesion Formation

Rice lesion mimic mutants (LMMs) form spontaneous lesions on the leaves during vegetative growth without pathogenic infections. The rice LMM group includes various mutants, including spotted leaf mutants, brown leaf mutants, white-stripe leaf mutants, and other lesion-phenotypic mutants. These LMM mutants exhibit a common phenotype of lesions on the leaves linked to chloroplast destruction caused by the eruption of reactive oxygen species (ROS) in the photosynthesis process. This process instigates the hypersensitive response (HR) and programmed cell death (PCD), resulting in lesion formation. The reasons for lesion formation have been studied extensively in terms of genetics and molecular biology to understand the pathogen and stress responses. In rice, the lesion phenotypes of most rice LMMs are inherited according to the Mendelian principles of inheritance, which remain in the subsequent generations. These rice LMM genetic traits have highly developed innate self-defense mechanisms. Thus, although rice LMM plants have undesirable agronomic traits, the genetic principles of LMM phenotypes can be used to obtain high grain yields by deciphering the efficiency of photosynthesis, disease resistance, and environmental stress responses. From these ailing rice LMM plants, rice geneticists have discovered novel proteins and physiological causes of ROS in photosynthesis and defense mechanisms. This review discusses recent studies on rice LMMs for the Mendelian inheritances, molecular genetic mapping, and the genetic definition of each mutant gene.

PREMATURE SENESCENCE LEAF 50 Promotes Heat Stress Tolerance in Rice (Oryza sativa L.)

Background Heat stress is a major environmental factor that could induce premature leaf senescence in plants. So far, a few rice premature senescent leaf mutants have been reported to involve in heat tolerance. Findings We identified a premature senescence leaf 50 (psl50) mutant that exhibited a higher heat susceptibility with decreased survival rate, over-accumulated hydrogen peroxide (H2O2) content and increased cell death under heat stress compared with the wild-type. The causal gene PREMATURE SENESCENCE LEAF 50 (PSL50) was isolated by using initial map-based resequencing (IMBR) approach, and we found that PSL50 promoted heat tolerance probably by acting as a modulator of H2O2 signaling in response to heat stress in rice (Oryza sativa L.). Conclusions PSL50 negatively regulates heat-induced premature leaf senescence in rice.

Premature Senescence Leaf 50 Promotes Heat Stress Tolerance in Rice (Oryza Sativa L.)

BackgroundHeat stress is a major environmental factor that could induce premature leaf senescence in plants. So far, few rice premature senescent leaf mutants have been reported to involve in heat tolerance.FindingsWe identified a premature senescence leaf 50 (psl50) mutant that exhibited a higher heat susceptibility with decreased survival rate, over-accumulated hydrogen peroxide (H2O2) content and increased cell death under heat stress compared with the wild-type. The causal gene PREMATURE SENESCENCE LEAF 50 (PSL50) was isolated by using initial map-based resequencing (IMBR) approach, and we found that PSL50 promoted heat tolerance probably by acting as a modulator of H2O2 signaling in response to heat stress in rice (Oryza sativa L.).ConclusionsPSL50 negatively regulates heat-induced premature leaf senescence in rice.

Metabolomic and transcriptomic analyses of mutant yellow leaves provide insights into pigment synthesis and metabolism in Ginkgo biloba

Background Ginkgo (Ginkgo biloba L.) is an excellent landscape species. Its yellow-green leaf mutants are ideal materials for research on pigment synthesis, but the regulatory mechanism of leaf coloration in these ginkgo mutants remains unclear. Results We compared the metabolomes and transcriptomes of green and mutant yellow leaves of ginkgo over the same period in this study. The results showed that the chlorophyll content of normal green leaves was significantly higher than that of mutant yellow leaves of ginkgo. We obtained 931.52M clean reads from different color leaves of ginkgo. A total of 283 substances in the metabolic profiles were finally detected, including 50 significantly differentially expressed metabolites (DEMs). We identified these DEMs and 1361 differentially expressed genes (DEGs), with 37, 4, 3 and 13 DEGs involved in the photosynthesis, chlorophyll, carotenoid, and flavonoid biosynthesis pathways, respectively. Moreover, integrative analysis of the metabolomes and transcriptomes revealed that the flavonoid pathway contained the upregulated DEM (−)-epicatechin. Fourteen DEGs from the photosynthesis pathway were positively or negatively correlated with the DEMs. Conclusions Our findings suggest a complex metabolic network in mutant yellow leaves. This study will provide a basis for studies of leaf color variation and regulation.

Transcriptome analysis of an albino mutant in Haworthia cooperi var. pilifera

ABSTRACTPhotosynthetic organisms appear green due to the accumulation of chlorophyll (Chl) pigments in their chloroplasts. Although the genes encoding key enzymes related to Chl biosynthesis have been well characterized in herbaceous plants, such as rice, Arabidopsis and maize, white leaf mutants have not yet been fully studied in succulent plants. In this work, we explored the molecular mechanism of leaf color formation in an albino mutant (HUA) of Haworthia cooperi var. pilifera. We investigated the differentially expressed genes (DEGs) between HUA and control plants (wild type, LV) by transcriptome sequencing. Approximately 2,586 genes (1,996 downregulated and 590 upregulated) were found to be differentially expressed in HUA compared with LV using a threshold of ratio change ≥ 2 and false discovery rate (FDR) ≤0.05. GO analysis predicted that these DEGs participate in 12 cellular component, 20 biological process and 13 molecular function terms. Among the DEGs were well-recognized genes associated with chloroplast division and the biosynthesis of plant pigments, including chlorophyll, carotenoids and anthocyanin, as well as various transcription factor families. Overall, these results can help confirm the molecular regulatory mechanisms controlling leaf pigmentation and provide a comprehensive resource for breeding colorful leaf phenotypes in succulent plants.

Widely Targeted Metabolomic and Transcriptomic Analyses of a Novel Albino Tea Mutant of “Rougui”

Albino tea mutants with specific shoot colors (white or yellow) have received increasing attention from researchers due to their unique phenotypes, beneficial metabolites, and special flavor. In this study, novel natural yellow leaf mutants of the same genetic background of “Rougui” were obtained, and the transcriptome and metabolite profiles of the yellow leaf mutant (YR) and original green cultivar (GR) were investigated. A total of 130 significantly changed metabolites (SCMs) and 55 differentially expressed genes (DEGs) were identified in YR compared to GR. The leaf coloration of YR was primarily affected by pigment metabolism including of chlorophyll, carotenoids, and flavonoids, and the co-expression of three heat shock proteins (HSPs) and four heat shock transcription factors (HSFs) may also regulate leaf coloration by affecting chloroplast biogenesis. Of the 130 SCMs, 103 showed clearly increased abundance in YR, especially nucleotides and amino acids and their derivatives and flavonoids, suggesting that YR may be an ideal albino tea germplasm for planting and breeding. Our results may help to characterize the leaf coloration and metabolic mechanism of albino tea germplasm.

Zebra leaf 15, a receptor-like protein kinase involved in moderate low temperature signaling pathway in rice

Background Zebra leaf mutants are an important resource for studying leaf colour in rice. In most such mutants, the zebra leaf phenotype results from defective chloroplast biogenesis. The molecular mechanism by which zebra leaves develop remains unclear, so additional zebra-leaf mutants need to be identified. Results We isolated a novel rice zebra-leaf mutant, named zebra leaf 15 (z15), which showed transversely striped leaves with yellow-green or white-green sectors, in which chloroplast structure was disturbed. Transmission electron microscopy revealed that the structure of various organelles was impaired in yellow/white sectors. Z15, a single-copy gene in the rice genome, encodes a receptor-like protein kinase. Subcellular localization analysis indicates that Z15 and z15 are localized on the plasma membrane. The expression of Z15 is induced by moderate low temperature (18 °C). The mutation of Z15 influenced the expression of two downstream genes, OsWRKY71 and OsMYB4, that were responsive to moderate low temperature. The results show that Z15 plays a crucial role in the early stages of the response to moderate low temperature in rice. Conclusions We identified a novel zebra-leaf mutant (z15) that impaired chloroplast structure in rice, LOC_Os05g12680, encoding a receptor-like protein kinase. Further study indiceted that Z15 plays a crucial role in the early stages of the response to moderate low temperature in rice.