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Corky split vein can develop under long-term boron deficient conditions in Citrus sinensis L. Osbeck cv. Newhall. This symptom only occurs in the upper rather than the lower epidermis of old leaves. Our previous study demonstrated that vascular hypertrophy was involved in the symptoms, and the 3rd developmental stage of corky split vein (BD3) was the critical stage for phenotype formation. Here, we performed an intensive study on the BD3 vein and its control sample (CK3 vein). A lignin test demonstrated that the lignin content in BD3 vein was approximately 1.7 times more than the CK3 vein. Anatomical investigation of the corky split vein indicated that the upper epidermis was destroyed by overgrowing vascular cells, and the increased lignin may contribute to vascular cell differentiation and wounding-induced lignification. In a subsequent small RNA sequencing of the BD3 and CK3 veins, 99 known miRNAs and 22 novel miRNAs were identified. Comparative profiling of these miRNAs demonstrated that the 57 known miRNAs and all novel miRNAs exhibited significant expression differences between the two small RNAs libraries of the BD3 and CK3 veins. Associated with our corresponding digital gene expression data, we propose that the decreased expression of two miRNAs, csi-miR156b and csi-miR164, which leads to the up-regulation of their target genes, SPLs (csi-miR156b-targeted) and CUC2 (csi-miR164-targeted), may promote vascular cell division and orderless stage transition in old leaves. [ABSTRACT FROM AUTHOR]

The direct analysis in real-time (DART) ion source and HPLC-electrospray mass spectrometry were applied in non-targeted metabolomic analyses of fruits of an orange bud mutant, 'Hong Anliu' along with its parental wild-type, 'Anliu'. Fruits of the two isogenic cultivars were sampled at three different ripening stages, i.e. 120, 170 and 220 days after flowering. More than 130 metabolites were tentatively identified, including acids, sugars, flavonoids, alkaloids, limonoids, coumarins, amino acids, and plant hormones. Metabolomic analyses revealed that, compared to its wild type, the bud mutant fruit is characterized by higher levels of monosaccharides and disaccharides and lower levels of organic acids such as citric acid, malic acid and quinic acid, which agrees well with the anticipated fruit quality benefits of the mutation. In addition, many secondary metabolites, such as flavonoids, showed significant differences between the two genotypes, indicating that the whole fruit metabolome is significantly changed due to the bud mutation. This study provided a comprehensive assessment of metabolites in orange fruits, and revealed metabolomic differences in fruits between two isogenic orange genotypes. The results are helpful for understanding how the bud mutation in 'Hong Anliu' impacts the physiological and biochemical processes of orange fruits. [ABSTRACT FROM AUTHOR]

Distinguishing a bud mutant from its parental genotype using conventional molecular markers is extremely difficult because they are thought to be genetically near-identical owing to the nature of somatic mutations that give rise to the bud mutant phenotype. In this study, array-comparative genome hybridization (array-CGH) was used to investigate the genetic variation between a sweet orange bud mutant 'Hong Anliu' and its parental type 'Anliu'. Surprisingly, 25 candidate genes were shown to exhibit gene dosage variations, with 18 being underrepresented and 7 overrepresented in the bud mutant in comparison with the parental type. These gene dosage variations were validated by quantitative PCR. Interestingly, however, the transcription levels of some of the corresponding genes were not significantly different between the two genotypes. The detection of gene dosage variations in at least 25 candidate genes between 'Hong Anliu' and 'Anliu' may explain in part the genetic difference responsible for the phenotypic deviation of the bud mutant from its parental cultivar. Our findings also suggest that array-CGH is a powerful technology that can be used for detection of genome-wide variations among near-identical genotypes such as bud mutants and their parental cultivars. [ABSTRACT FROM AUTHOR]

Abstract: An integrative analysis of transcriptome and proteome was performed to identify differential genes/proteins of a red-flesh sweet orange Cara Cara in comparison with a common cultivar Newhall at ripening stages. At the transcript level, gene expression was measured with Massively Parallel Signature Sequencing (MPSS), and 629 genes of these two sweet orange cultivars differed by two fold or more (FDR<0.001). At the protein level, a combination of 2DE and MALDI-TOF-TOF MS identified 48 protein spots differed in relative abundance (P<0.05). The data obtained from comparing transcriptome with proteome showed a poor correlation, suggesting the necessity to integrate both transcriptomic and proteomic approaches in order to get a comprehensive molecular characterization. Function analysis of the differential genes/proteins revealed that a set of candidates was associated with carotenoid biosynthesis and the regulation. Overall, some intriguing genes/proteins were previously unrecognized related with the formation of red-flesh trait, which provided new insights into molecular processes regulating lycopene accumulation in a red-flesh sweet orange. In addition, some genes/proteins were found to be different in expression patterns between the Cara Cara and another red-flesh sweet orange Hong Anliu, and their potential roles were further discussed in the present study. [Copyright &y& Elsevier]

Here, a comprehensive proteomic analysis of the chromoplasts purified from sweet orange using Nycodenz density gradient centrifugation is reported. A GeLC-MS/MS shotgun approach was used to identify the proteins of pooled chromoplast samples. A total of 493 proteins were identified from purified chromoplasts, of which 418 are putative plastid proteins based on in silico sequence homology and functional analyses. Based on the predicted functions of these identified plastid proteins, a large proportion (∼60%) of the chromoplast proteome of sweet orange is constituted by proteins involved in carbohydrate metabolism, amino acid/protein synthesis, and secondary metabolism. Of note, HDS (hydroxymethylbutenyl 4-diphosphate synthase), PAP (plastid-lipid-associated protein), and psHSPs (plastid small heat shock proteins) involved in the synthesis or storage of carotenoid and stress response are among the most abundant proteins identified. A comparison of chromoplast proteomes between sweet orange and tomato suggested a high level of conservation in a broad range of metabolic pathways. However, the citrus chromoplast was characterized by more extensive carotenoid synthesis, extensive amino acid synthesis without nitrogen assimilation, and evidence for lipid metabolism concerning jasmonic acid synthesis. In conclusion, this study provides an insight into the major metabolic pathways as well as some unique characteristics of the sweet orange chromoplasts at the whole proteome level. [ABSTRACT FROM PUBLISHER]

Interveinal chlorosis in old leaves is a common occurrence in citrus orchards in southern China. The present study investigates the 'Langfeng' navel orange (LF, Citrus sinensis) grafted onto a Trifoliate orange (TO, Poncirus trifoliata) rootstock, which exhibits healthy green leaves, and the 'Newhall' navel orange (NHE, C. sinensis) grafted onto TO, which has typical magnesium (Mg) deficiency-induced chlorosis. Chemical analysis of the rhizosphere soil revealed that the pH values were around 3.92 and that both Mg and calcium (Ca) were significantly deficient in the rhizosphere soil of both grafting combinations (LF/TO and NHE/TO). Furthermore, the chlorotic leaves of NHE/TO had significantly lower levels of Mg, Ca, and phosphorus (P), and the green leaves of NHE/TO had significantly lower levels of Mg and Ca compared to the green leaves of the LF/TO. This suggests that Mg deficiency may be the primary cause of chlorosis in NHE/TO. A greenhouse study using the same graft combinations showed that the LF/TO plants had better growth than the NHE/TO, possibly by promoting Mg uptake and/or improving Mg distribution to leaves, thereby increasing carbon dioxide (CO 2) assimilation and photosynthesis, optimizing carbohydrate distribution, and increasing plant biomass. This results in a phenotype that is tolerant to Mg deficiency. In conclusion, these findings suggest that the LF navel orange could be utilized in the development of new citrus varieties with improved Mg-use efficiency. • Interveinal chlorosis is common in southern China citrus orchards. • Study compares "Langfeng" navel orange (LF) on Trifoliate orange rootstock (TO) to "Newhall" navel orange (NHE) on TO. • Soil analysis showed Mg and Ca deficiencies and NHE/TO had lower levels of Mg, Ca, and P in chlorotic leaves. • Greenhouse study showed better growth in LF/TO plants, indicating improved Mg uptake and tolerance to Mg deficiency. • Findings suggest LF navel orange can be used in new citrus varieties with improved Mg-use efficiency. [ABSTRACT FROM AUTHOR]

• Potassium (K) fertilizer improved fruit quality in Cara Cara navel fruit. • K enhanced sugar accumulations by improving sucrose metabolism and sink strength. • K fertilizer increased citrate accumulations partially by promoting its synthesis. Sugars and organic acid are key factors for sensory properties of fruit quality. Potassium (K) is an essential macroelement and is also known as quality element. This study aims to investigate how K affects quality improvement particularly sucrose, fructose, glucose and citrate accumulations in Cara Cara navel orange. K fertilizer increased fruit sucrose, fructose, glucose and citrate concentrations and the ratios of total soluble sugars and citrate, particularly the ratios increased more in the treatment of 0.50 kg/plant K fertilizer. These results showed that suitable amount of K fertilizer could improve fruit quality of Cara Cara navel orange. Further study showed that, at early stage of fruit development, K fertilizer played more important roles in degrading sucrose due to the increased activities of sucrose-degrading enzymes including invertase and sucrose synthase-cleavage activity. Conversely, at late stage of fruit development, K fertilizer played more important roles in re-synthesizing sucrose due to the higher activities of sucrose-synthesizing enzymes including sucrose synthase-synthetic activity and sucrose phosphate synthase. The above results suggested that the upregulations of sucrose-degrading and sucrose-synthesizing enzyme activities caused by K fertilizer were conducive to improving sucrose metabolism and sink strength, and then increased the concentrations of sucrose, fructose and glucose in fruit. K fertilizer increased the activities of citrate-synthesizing enzymes including citrate synthetase and phosphoenolpyruvate carboxylase, but had no significant impacts on the activities of citrate-degrading enzyme, indicating that K fertilizer increased citrate accumulations at least partially by promoting its synthesis. This study finally suggested that K fertilizer improved the accumulations of soluble sugar and citrate in Cara Cara navel orange. [ABSTRACT FROM AUTHOR]