An S-locus F-box protein as pollen S determinant targets non-self S-RNase underlying self-incompatibility in Citrus.

Self-incompatibility (SI) is a crucial mechanism that prevents self-fertilization and inbreeding in flowering plants. Citrus exhibits SI regulated by a polymorphic S-locus containing an S-RNase gene and multiple S-locus F-box (SLF) genes. It has been documented that S-RNase functions as the pistil S determinant, but there is no direct evidence that the SLF genes closely linked with S-RNase function as pollen S determinants in Citrus. This study assembled the genomes of two pummelo (Citrus grandis) plants, obtained three novel complete and well-annotated S-haplotypes, and isolated 36 SLF or SLF-like alleles on the S-loci. Phylogenetic analysis of 138 SLFs revealed that the SLF genes were classified into 12 types, including six types with divergent or missing alleles. Furthermore, transformation experiments verified that the conserved S6-SLF7a protein can lead to the transition of SI to self-compatibility by recognizing non-self S8-RNase in 'Mini-Citrus' plants (S7S8 and S8S29, Fortunella hindsii), a model plant for citrus gene function studies. In vitro assays demonstrated interactions between SLFs of different S haplotypes and the Skp1-Cullin1-F-box subunit CgSSK1 protein. This study provides direct evidence that SLF controls the pollen function in Citrus, demonstrating its role in the 'non-self recognition' SI system.

Genome-wide identification, classification and analysis of HD-ZIP gene family in citrus, and its potential roles in somatic embryogenesis regulation.

The homeodomain-leucine zipper (HD-Zip) transcription factors, which belong to a class of Homeobox proteins, has been reported to be involved in different biological processes of plants, including growth and development, photomorphogenesis, flowering, fruit ripening and adaptation responses to environmental stresses. In this study, 27 HD-Zip genes (CsHBs) were identified in Citrus. Based on the phylogenetic analysis and characteristics of individual gene or protein, the HD-Zip gene family in Citrus can be classified into 4 subfamilies, i.e. HD-Zip I, HD-Zip II, HD-Zip III, and HD-Zip IV containing 16, 2, 4, and 5 members respectively. The digital expression patterns of 27 HD-Zip genes were analyzed in the callus, flower, leaf and fruit of Citrus sinensis. The qRT-PCR and RT-PCR analyses of six selected HD-Zip genes were performed in six citrus cultivars with different embryogenic competence and in the embryo induction stages, which revealed that these genes were differentially expressed and might be involved in citrus somatic embryogenesis (SE). The results exhibited that the expression of CsHB1 was up-regulated in somatic embryo induction process, and its expression was higher in citrus cultivars with high embryogenic capacity than in cultivars recalcitrant to form somatic embryos. Moreover, a microsatellite site of three nucleotide repeats was found in CsHB1 gene among eighteen citrus genotypes, indicating the possible association of CsHB1 gene to the capacity of callus induction.

Comparative transcriptome analyses between a spontaneous late-ripening sweet orange mutant and its wild type suggest the functions of ABA, sucrose and JA during citrus fruit ripening.

A spontaneous late-ripening mutant of 'Jincheng' (C. sinensis L. Osbeck) sweet orange exhibited a delay of fruit pigmentation and harvesting. In this work, we studied the processes of orange fruit ripening through the comparative analysis between the Jincheng mutant and its wild type. This study revealed that the fruit quality began to differ on 166th days after anthesis. At this stage, fruits were subjected to transcriptome analysis by RNA sequencing. 13,412 differentially expressed unigenes (DEGs) were found. Of these unigenes, 75.8% were down-regulated in the wild type, suggesting that the transcription level of wild type was lower than that of the mutant during this stage. These DEGs were mainly clustered into five pathways: metabolic pathways, plant-pathogen interaction, spliceosome, biosynthesis of plant hormones and biosynthesis of phenylpropanoids. Therefore, the expression profiles of the genes that are involved in abscisic acid, sucrose, and jasmonic acid metabolism and signal transduction pathways were analyzed during the six fruit ripening stages. The results revealed the regulation mechanism of sweet orange fruit ripening metabolism in the following four aspects: First, the more mature orange fruits were, the lower the transcription levels were. Second, the expression level of PME boosted with the maturity of the citrus fruit. Therefore, the expression level of PME might represent the degree of the orange fruit ripeness. Third, the interaction of PP2C, PYR/PYL, and SnRK2 was peculiar to the orange fruit ripening process. Fourth, abscisic acid, sucrose, and jasmonic acid all took part in orange fruit ripening process and might interact with each other. These findings provide an insight into the intricate process of sweet orange fruit ripening.

Comparative transcript profiling of gene expression between seedless Ponkan mandarin and its seedy wild type during floral organ development by suppression subtractive hybridization and cDNA microarray.

BACKGROUND: Seedlessness is an important agronomic trait for citrus, and male sterility (MS) is one main cause of seedless citrus fruit. However, the molecular mechanism of citrus seedlessness remained not well explored. RESULTS: An integrative strategy combining suppression subtractive hybridization (SSH) library with cDNA microarray was employed to study the underlying mechanism of seedlessness of a Ponkan mandarin seedless mutant (Citrus reticulata Blanco). Screening with custom microarray, a total of 279 differentially expressed clones were identified, and 133 unigenes (43 contigs and 90 singletons) were obtained after sequencing. Gene Ontology (GO) distribution based on biological process suggested that the majority of differential genes are involved in metabolic process and respond to stimulus and regulation of biology process; based on molecular function they function as DNA/RNA binding or have catalytic activity and oxidoreductase activity. A gene encoding male sterility-like protein was highly up-regulated in the seedless mutant compared with the wild type, while several transcription factors (TFs) such as AP2/EREBP, MYB, WRKY, NAC and C2C2-GATA zinc-finger domain TFs were down-regulated. CONCLUSION: Our research highlighted some candidate pathways that participated in the citrus male gametophyte development and could be beneficial for seedless citrus breeding in the future.

Transcriptional profiling of genes involved in embryogenic, non-embryogenic calluses and somatic embryogenesis of Valencia sweet orange by SSH-based microarray.

Somatic embryogenesis (SE) is a most promising technology that is used for in vitro germplasm conservation and genetic improvement via biotechnological approaches in citrus. Herein, three suppression subtractive hybridization (SSH) libraries were constructed using calluses of Citrus sinensis cv. 'Valencia' to explore the molecular mechanisms that underlie the SE in citrus. A total of 880 unisequences were identified by microarray screening based on these three SSH libraries. Gene ontology analysis of the differentially expressed genes indicated that nucleolus associated regulation and biogenesis processes, hormone signal transduction, and stress factors might be involved in SE. Transcription factors might also play an important role. LEC1/B3 domain regulatory network genes (LEC1, L1L, FUS3, ABI3, and ABI5) were isolated in citrus SE. Some new transcription factors associated with citrus SE, like a B3 domain containing gene and HB4, were identified. To understand the influence of these isolated genes on SE competence, their expression profiles were compared among callus lines of seven citrus cultivars with different SE competence. The expression dynamics suggested that these genes could be necessary for the SE initiation and might play a role in embryogenic competence maintenance in different cultivars. On the basis of gene expression profiles, an overview of major physiological and biosynthesis processes at different developmental stages during citrus SE is presented. For the first time, these data provide a global resource for transcriptional events important for SE in citrus, and the specific genes offer new information for further investigation on citrus SE maintenance and development.

Hydrogen sulfide regulates cardiac function and structure in adriamycin-induced cardiomyopathy.

BACKGROUND: The present study was designed to investigate if hydrogen sulfide (H2S), a novel gasotransmitter, might have a regulatory effect on cardiac function and structure, as well as oxidative stress, in adriamycin (ADR)-induced cardiomyopathy. METHODS AND RESULTS: Hemodynamic measurements, histopathological examination and stereological ultrastructural analysis of mitochondria in ADR-treated rats showed characteristics of cardiomyopathy with remarkable greater size and smaller number of cardiomyocytic mitochondria and a significantly low H2S content in plasma and myocardium, but increased levels of thiobarbituric acid reactive substance (TBARs) and decreased superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities in plasma and myocardium compared with controls (P<0.01). However, administration of the H2S donor, NaHS, markedly improved cardiac function, as demonstrated by elevated left ventricular developed pressure (+/-LVdp/dtmax; P<0.01) with ameliorated morphological alterations in the myocardium. Myocardial TBARs content decreased, whereas the activities of SOD and GSH-Px increased (P<0.01 and P<0.05, respectively). CONCLUSIONS: Downregulation of endogenously-generated H2S is probably involved in the pathogenesis of ADR-induced cardiomyopathy, whereby H2S reduces lipid peroxidation, increases antioxidation, and inhibits oxidative stress injury.

[Effects of glucagon like peptide-1 treatment on the alveolar capillary basal lamina in Otsuka Long-Evans Tokushima Fatty rats].

OBJECTIVE: To observe and quantitatively analyze the effect of glucagon like peptide-1 (GLP-1) on the alveolar capillary basal lamina in spontaneous type 2 diabetes mellitus animal model Otsuka Long-Evans Tokushima Fatty (OLETF) rats. METHODS: Experimental rats were divided into three groups: OLETF group, GLP-1-treated group (OLETF/G group), and Long-Evans Tokushima Otsuka group (LETO group) as control. The ultrastructure and thickness of the alveolar capillary basal lamina in the rats were examined by transmission electron microscopy and morphometry methods. RESULTS: The fused basal lamina (F-BL) of the alveolar capillary endothelium and type I epithelial basal lamina, and the alveolar capillary endothelium basal lamina (Cap-BL) were thickened in OLETF rats than those of LETO rats [(110.60+/-14.14) nm vs (57.30+/-11.08) nm, and (118.40+/-19.12) nm vs (66.80+/-8.63) nm, P<0.01]. F-BL and Cap-BL were thinned in the OLETF/G group as compared with OLETF group [(79.70+/-5.44) nm vs (110.60+/-14.14) nm and (69.80 +/-3.32) nm vs (118.40+/-19.12) nm, P<0.01]. CONCLUSION: Our studies suggest the existence of ultrastructural changes of alveolar capillary basal lamina in OLETF rats. GLP-1 intervention decreases the damage of alveolar capillary basal lamina in OLETF rats.

[Pathological features of light chain nephropathy].

OBJECTIVE: To investigate the pathologic features and diagnostic algorithm of light chain nephropathy (LCN). METHODS: Seven cases of LCN were studied by light microscopy, electron microscopy and immunolabeling of light chains (kappa, lambda) by immunofluorescence and immunoelectron microscopy. RESULTS: The histopathology of 7 cases by light microscopy was variable, with 3 cases showing nodular glomerulosclerosis, 1 case showing mild to moderate mesangial proliferation, and 3 cases showing cast nephropathy with minimal glomerular change. Immunofluorescence study revealed positive staining of a single type of light chain in mesangium (nodular pattern) or along glomerular basement membrane (linear), along tubular basement membrane and around arteriolar walls in all the 7 cases. Ultrastructurally, electron-dense granular deposits were identified in mesangium, subendothelial aspect of glomerular basement membrane, outer aspect of tubular basement membrane and arteriolar walls. Immunogold labeling of light chains showed distinct labeling of a single type light chain in the granular electron-dense materials (5 cases being kappa-positive and 2 being lambda-positive). CONCLUSIONS: LCN typically shows nodular glomerulosclerosis. The ultrastructural change is characteristic and important for diagnosis. Immunolabeling of light chains by immunofluorescence and immunoelectron microscopy carries further diagnostic value, especially in cases with minimal light microscopic change.