Jiongming Sui

A New GA-Insensitive Semidwarf Mutant of Rice (Oryza sativa L.) with a Missense Mutation in the SDG Gene

A semidwarf line of Indica rice, Xinguiai, was derived from the progeny of a cross between the double dwarf mutant Xinguiaishuangai and the wild-type variety Nanjing 6. The semidwarf phenotype was controlled by the semidwarf gene, sdg. The second sheath and shoot elongation responses of the dwarf mutant to exogenous gibberellin (GA3) showed that sdg was insensitive to gibberellin (GA), and its endogenous GAs content was higher than that in wild-type cultivars. The SDG gene was cloned by a map-based cloning method and sequencing analysis revealed that the coding region of sdg had a single nucleotide substitution resulting in a single amino acid change from alanine to threonine. A cleaved amplified polymorphic sequence marker was designed according to sequences from mutant and wild-type materials. This sequence marker could be used to distinguish wild types and mutants, and thus, could be used for molecular marker-assisted selection. The dwarf phenotype of the sdg mutant was restored to a normal phenotype by introducing the wild-type SDG gene. Rice transformation experiments and GUS staining demonstrated that the SDG gene was predominantly expressed in vegetative organs.

Isolation and characterization of a stress responsive small GTP-binding protein AhRabG3b in peanut (Arachis hypogaea L.)

Rab7 is a member of small GTP-binding protein family involved in intracellular vesicle trafficking from late endosome to vacuole, some of them are found to be responsive by different environmental stresses. Here we report the isolation of a Rab7 (RabG3b) cDNA from peanut (Arachis hypogaea). Overexpression of the open reading frame (ORF) of Rab7 cDNA encoding 205 amino acids in E. coli conferred the cells tolerance to various abiotic stresses. Transcription of AhRabG3b was differentially up-regulated by different environmental stimuli such as cold, dehydration, NaCl and the plant hormone ABA. Overexpression of the AhRabG3b exhibited enhanced tolerance to drought and salinity stresses in transgenic peanut. These results suggested that the AhRabG3b be a potential candidate gene responsible for both salinity and dehydration tolerance in cultivated peanut.

Generation of Peanut Drought Tolerant Plants by Pingyangmycin-Mediated In Vitro Mutagenesis and Hydroxyproline-Resistance Screening

In order to enlarge the potential resources of drought-tolerant peanuts, we conducted in vitro mutagenesis with Pingyangmycin (PYM) as the mutagen as well as directed screening on a medium supplemented with Hydroxyproline (HYP). After being extracted from mature seeds (cv. Huayu 20), the embryonic leaflets were cultured on somatic embryogenesis-induction medium with 4 mg/L PYM and the generated embryos were successively transferred to a germination medium with 4 and then 8 mmol/L HYP to screen HYP-tolerant plantlets. After that, these plantlets were grafted and transplanted to the experimental field. In the next generation, all seeds were sown in the field, and phenotype variation and trait segregation can be observed in most of the offspring (M2 generation). The M3 generation individuals were subjected to drought stress at the seedling stages. The activities of SOD and POD were substantially increased in eight offspring of 11 HYP-tolerant, regenerated plants than in their mutagenic parents. To determine the correlation between mutant phenotypes and genomic modification, we carried out a comparison of the DNA polymorphisms between the mutagenic parents and 13 M3 generation individuals from different HYP-tolerant, regenerated plants with SSR primers. Results showed that most mutants and parent plants had signs of polymorphisms. Under drought stress, some M3 generation individuals of 10 original HYP-tolerant, regenerated plants produced more pods than the mutagenic parent; twenty individuals among them produced >60 g pods/plant. M4-generation seeds were tested for quality characteristics by Near Infrared Spectroscopy (NIS) and nine individuals with higher protein content (>30%) and 21 individuals with higher oil content (>58%) were screened. We concluded that the use of PYM-based in vitro mutagenesis in combination with directed screening with HYP is effective for the creation of potential drought-tolerant mutants of peanut.

Generation of peanut mutants by fast neutron irradiation combined with in vitro culture

Induced mutations have played an important role in the development of new plant varieties. In this study, we investigated the effects of fast neutron irradiation on somatic embryogenesis combined with plant regeneration in embryonic leaflet culture to develop new peanut (Arachis hypogaea L.) germplasm for breeding. The dry seeds of the elite cultivar Luhua 11 were irradiated with fast neutrons at dosages of 9.7, 14.0 and 18.0 Gy. The embryonic leaflets were separated and incubated in a medium with 10.0-mg/l 2,4-D to induce somatic embryogenesis. Next, they were incubated in a medium with 4.0-mg/l BAP for plant regeneration. As the irradiation dosage increased, the frequency of both somatic embryo formation and plantlet regeneration decreased. The regenerated plantlets were grafted onto rootstocks and were transplanted into the field. Later, the mature seeds of the regenerated plants were harvested. The M2 generation plants from most of the regenerated cultivars exhibited variations and segregation in vigor, plant height, branch and pod number, pod size, and pod shape. To determine whether the phenotypes were associated with genomic modification, we compared the DNA polymorphisms between the wild-type plants and 19 M3-generation individuals from different regenerated plants. We used 20 pairs of simple sequence repeat (SSR) primers and detected polymorphisms between most of the mutants and the wild-type plants (Luhua 11). Our results indicate that using a combination of fast neutron irradiation and tissue culture is an effective approach for creating new peanut germplasm.

The Salinity Responsive Mechanism of a Hydroxyproline-Tolerant Mutant of Peanut Based on Digital Gene Expression Profiling Analysis.

Soil salinity seriously limits plant growth and yield. Strategies have been developed for plants to cope with various environmental stresses during evolution. To screen for the broad-spectrum genes and the molecular mechanism about a hydroxyproline-tolerant mutant of peanut with enhanced salinity resistance under salinity stress, digital gene expression (DGE) sequencing was performed in the leaves of salinity-resistant mutant (S2) and Huayu20 as control (S4) under salt stress. The results indicate that major transcription factor families linked to salinity stress responses (NAC, bHLH, WRKY, AP2/ERF) are differentially expressed in the leaves of peanut under salinity stress. In addition, genes related to cell wall loosening and stiffening (xyloglucan endotransglucosylase/hydrolases, peroxidases, lipid transfer protein, expansin, extension), late embryogenesis abundant protein family, fatty acid biosynthesis and metabolism (13-lipoxygenase omega-6 fatty acid desaturase, omega-3 fatty acid desaturase) and some previously reported stress-related genes encoding proteins such as defensin, universal stress protein, metallothionein, peroxidase etc, and some other known or unknown function stress related genes, have been identified. The information from this study will be useful for further research on the mechanism of salinity resistance and will provide a useful genomic resource for the breeding of salinity resistance variety in peanut.

RNA-seq analysis reveals the role of a small GTP-binding protein, Rab7, in regulating clathrin-mediated endocytosis and salinity-stress resistance in peanut

Small GTP-binding proteins, Rab7, are known to be responsive to abiotic stresses in plants, but the molecular mechanism is poorly understood. To investigate how AhRab7 increases resistance to salinity stress in peanut, this study compared a transgenic genotype (S5) that overexpressed the AhRab7 gene and that had high salinity resistance with a non-transgenic genotype (S7) that had low salinity resistance. Digital gene expression (DGE) sequencing was performed with leaves of S5 and S7 before and after salinity-stress treatment. In total, 2697 differentially expressed genes (DEGs) were identified between S5 and S7, and KEGG enrichment analyses showed that the DEGs are involved pathways including endocytosis, lysosome, hormone signaling, phosphatidylinositol signaling, calcium, and others. Among them, 164 were differentially regulated after salinity-stress treatment. Of 164 DEGs, 110 were responsive to salinity stress in S5 and/or S7. The 110 DEGs included genes that encode the following kinds of transcription factors and proteins known to be involved in resistance to salinity stress: WRKY, NAC, MYM-type zinc finger, late embryogenesis abundant proteins, lipid transfer protein, 1-cys peroxiredoxin, aquaporin, oleosin, and others. AhRab7 gene might mediate signaling pathways including phosphatidylinositol, calcium, abscisic acid, etc., and then regulate the expression of transcription factors and downstream genes for ROS scavenging in peanut. The results of this study will be useful for further investigations of the mechanism underlying the role of the AhRab7 gene in resistance to salinity stress in peanut.