Solving the regulation puzzle of periderm development using advances in fruit skin.

Periderm protects enlarged organs of most dicots and gymnosperms as a barrier to water loss and disease invasion during their secondary growth. Its development undergoes a complex process with genetically controlled and environmental stress-induced characters. Different development of periderm makes the full and partial russet of fruit skin, which diverges in inheritance with qualitative and quantitative characters, respectively, in pear pome. In addition to its specific genetics, fruit periderm has similar development and structure as that of stem and other organs, making it an appropriate material for periderm research. Recently, progress in histochemical as well as transcriptome and proteome analyses, and quantitative trait locus (QTL) mapping have revealed the regulatory molecular mechanism in the periderm based on the identification of switch genes. In this review, we concentrate on the periderm development, propose the conservation of periderm regulation between fruit and other plant organs based on their morphological and molecular characteristics, and summarize a regulatory network with the elicitors and repressors for the tissue development. Spontaneous programmed-cell death (PCD) or environmental stress produces the original signal that triggers the development of periderm. Spatio-temporal specific PCD produced by PyPPCD1 gene and its homologs can play a key role in the coordinated regulation of cell death related tissue development.

Exploring candidate genes for pericarp russet pigmentation of sand pear (Pyrus pyrifolia) via RNA-Seq data in two genotypes contrasting for pericarp color.

Sand pear (Pyrus pyrifolia) russet pericarp is an important trait affecting both the quality and stress tolerance of fruits. This trait is controlled by a relative complex genetic process, with some fundamental biological questions such as how many and which genes are involved in the process remaining elusive. In this study, we explored differentially expressed genes between the russet- and green-pericarp offspring from the sand pear (Pyrus pyrifolia) cv. 'Qingxiang' × 'Cuiguan' F1 group by RNA-seq-based bulked segregant analysis (BSA). A total of 29,100 unigenes were identified and 206 of which showed significant differences in expression level (log2fold values>1) between the two types of pericarp pools. Gene Ontology (GO) analyses detected 123 unigenes in GO terms related to 'cellular_component' and 'biological_process', suggesting developmental and growth differentiations between the two types. GO categories associated with various aspects of 'lipid metabolic processes', 'transport', 'response to stress', 'oxidation-reduction process' and more were enriched with genes with divergent expressions between the two libraries. Detailed examination of a selected set of these categories revealed repressed expressions of candidate genes for suberin, cutin and wax biosynthesis in the russet pericarps.Genes encoding putative cinnamoyl-CoA reductase (CCR), cinnamyl alcohol dehydrogenase (CAD) and peroxidase (POD) that are involved in the lignin biosynthesis were suggested to be candidates for pigmentation of sand pear russet pericarps. Nine differentially expressed genes were analyzed for their expressions using qRT-PCR and the results were consistent with those obtained from Illumina RNA-sequencing. This study provides a comprehensive molecular biology insight into the sand pear pericarp pigmentation and appearance quality formation.

Pigmentation in sand pear (Pyrus pyrifolia) fruit: biochemical characterization, gene discovery and expression analysis with exocarp pigmentation mutant.

Exocarp color of sand pear is an important trait for the fruit production and has caused our concern for a long time. Our previous study explored the different expression genes between the two genotypes contrasting for exocarp color, which indicated the different suberin, cutin, wax and lignin biosynthesis between the russet- and green-exocarp. In this study, we carried out microscopic observation and Fourier transform infrared spectroscopy analysis to detect the differences of tissue structure and biochemical composition between the russet- and green-exocarp of sand pear. The green exocarp was covered with epidermis and cuticle which was replaced by a cork layer on the surface of russet exocarp, and the chemicals of the russet exocarp were characterized by lignin, cellulose and hemicellulose. We explored differential gene expression between the russet exocarp of 'Niitaka' and its green exocarp mutant cv. 'Suisho' using Illumina RNA-sequencing. A total of 559 unigenes showed different expression between the two types of exocarp, and 123 of them were common to the previous study. The quantitative real time-PCR analysis supports the RNA-seq-derived gene with different expression between the two types of exocarp and revealed the preferential expression of these genes in exocarp than in mesocarp and fruit core. Gene ontology enrichment analysis revealed divorced expression of lipid metabolic process genes, transport genes, stress responsive genes and other biological process genes in the two types of exocarp. Expression changes in lignin metabolism-related genes were consistent with the different pigmentation of russet and green exocarp. Increased transcripts of putative genes involved the suberin, cutin and wax biosynthesis in 'Suisho' exocarp could facilitate deposition of the chemicals and take a role in the mutant trait responsible for the green exocarp. In addition, the divorced expression of ATP-binding cassette transporters involved in the trans-membrane transport of lignin, cutin, and suberin precursors suggests that the transport process could also affect the composition of exocarp and take a role in the regulation of exocarp pigmentation. Results from this study provide a base for the analysis of the molecular mechanism underlying sand pear russet/green exocarp mutation, and presents a comprehensive list of candidate genes that could be used to further investigate the trait mutation at the molecular level.

[Effects of water temperature and feeding on respiratory metabolism of juvenile Salvelinus fontinalus].

The oxygen consumption and ammonia excretion rates of juvenile brook trout (Salvelinus fontinalus) under satiation and starvation were measured at different levels of water temperature [(5.5 +/- 0.5), (8.5 +/- 0.5), (11.5 +/- 0.5), (14.5 +/- 0.5), (17.5 +/- 0.5) degrees C], aimed to study the effects of water temperature and feeding on the respiratory metabolism of the fish. Under satiation, the oxygen consumption and ammonia excretion rates of juvenile S. fontinalus at the five temperature levels increased rapidly to the maximum, and then decreased gradually to the initial state. The regression equations of oxygen consumption rate (OR) and ammonia excretion rate (NR) to water temperature (t) were OR = -0.0601 t4 + 2.5542 t3 - 39.256 t2 + 276.26 t - 598.75 (R2 = 1, 4.5 degrees C < t < 17.5 degrees C) and NR = - 0.0020 t4 + 0.0826 t3 - 1.2318 t2 + 8.6186 t - 18.838 (R2 = 1, 4.5 degrees C < t < 17.5 degrees C), respectively. Under starvation, the regression equations were OR = 13.723 t(0.9738) (R2 = 0.9974, 4.5 degrees C < t < 17.5 degrees C) and NR = 0.1687 t(1.0896) (R2 = 0.9977, 4.5 degrees C < t < 17.5 degrees C), respectively. The optimal temperature range was 11.5 degrees C-14.5 degrees C. The juvenile S. fontinalus in starvation was heavily depended on fat and carbohydrates.