Genome-wide analysis of the bZIP gene family and the role of AchnABF1 from postharvest kiwifruit (Actinidia chinensis cv. Hongyang) in osmotic and freezing stress adaptations.

Chilling injury (CI) is a barrier to the refrigeration of kiwifruit, resulting in decreased fruit quality and increased nutrient loss during storage. Understanding the molecular basis underlying the cold response and its regulation in refrigerated kiwifruit is therefore highly important. Basic (region) leucine zipper (bZIP) transcription factors (TFs) have been widely studied for their roles in abiotic stress resistance in various species. In this study, we identified 81 bZIP family proteins in kiwifruit and classified them into 11 groups. Further transcriptome analysis revealed that the expression of members of the AREB/ABF family was strongly induced by low temperature and abscisic acid (ABA). Ectopic expression of AchnABF1 enhanced plant cold tolerance by upregulating the expression of several key genes associated with ABA-dependent and ABA-independent pathways in Arabidopsis thaliana. Reactive oxygen species (ROS) metabolism was suggested to be involved in the AchnABF1-mediated osmotic stress response. For instance, enhanced ROS-scavenging ability was observed in transgenic plants with enhanced activity of catalase (CAT) and peroxidase (POD), which resulted in decreased in situ O2.- and H2O2 accumulation, ion leakage, and malondialdehyde (MDA) content under various abiotic stresses. In addition, AchnABF1 also participated in the osmotic stress response during both the germination and postgermination stages. We concluded that AchnABF1 may play an important role in kiwifruit during refrigeration.

Map-based cloning, identification and characterization of the w gene controlling white immature fruit color in cucumber (Cucumis sativus L.).

KEY MESSAGE: A single-nucleotide insertion resulted in a premature stop codon that is responsible for white immature fruit color in cucumber. Despite our previous progress in the mapping of the gene controlling white color in immature cucumber fruit and the identification of candidate genes, the specific gene that governs chlorophyll metabolism and its regulatory mechanism remains unknown. Here, we generated a mapping population consisting of 9497 F2 plants to delimit the controlling gene to an 8.2-kb physical interval that defines a sole candidate gene, APRR2. Sequencing the full-length DNA and cDNA of APRR2 allowed for identification of an allele, aprr2, encoding a truncated 101-amino acid protein due to a frameshift mutation and a premature stop codon. Gene structure prediction indicated that these 101 residues are located in a domain necessary for the function of the protein. The expression patterns of APRR2 were entirely consistent with the visual changes in green color intensity during fruit development. A microscopic observation of the fruit pericarp revealed fewer chloroplasts and a lower chloroplast chlorophyll storage capacity in Q24 (white) than in Q30 (green). A single-base insertion in the white color gene w, which leads to a premature stop codon, is hypothesized to have disabled the function of this gene in chlorophyll accumulation and chloroplast development. These findings contribute to basic research and the genetic improvement of fruit color.

Fine genetic mapping of the white immature fruit color gene w to a 33.0-kb region in cucumber (Cucumis sativus L.).

KEY MESSAGE: The white immature fruit color gene w was rapidly mapped to a 33.0-kb region to identify a valuable candidate gene that encodes peroxidase. The skin color of immature fruit is a crucial external trait of cucumbers, and white skin is shared by limited numbers of commercial cultivars. Herein, one BC1 population and two F2 segregating populations were constructed using four inbred parental lines (WD3 × B-2-2 and Q30 × Q24) to investigate the inheritance patterns and chromosomal locations of immature fruit color genes in cucumbers. Consequently, a single recessive gene, w, was identified that controls white immature fruit color. A total of 526 markers, which were derived from published genetic maps, two reference cucumber genomes ("9930" and GY14), and two parents (Q30 and Q24) for which whole-genome sequence information is available, were used to map the target gene w to a 33.0-kb region flanked by two SNP-based markers, ASPCR39262 and ASPCR39229, which are physically located at 39262450 and 39229482 of chromosome 3 ("9930" draft genome assembly), respectively. Gene prediction indicated that four potential genes were located in the target region. One gene that encodes peroxidase is likely to be a valuable candidate gene because quantitative real-time PCR revealed an eightfold difference in its transcriptional level, and several amino acid variations were found when the deduced amino acid sequence was aligned. A co-segregating marker was used synergistically to test its ability to predict the skin colors of 83 dark green/white germplasms, and the validity of its utility in marker-assisted selection was confirmed. Fine mapping of this locus will assist in cloning the gene and in marker-assisted breeding to develop dark green/white cucumber cultivars.

Control of mitochondrial activity by miRNAs.

Mitochondria supply energy for physiological function and they participate in the regulation of other cellular events including apoptosis, calcium homeostasis, and production of reactive oxygen species. Thus, mitochondria play a critical role in the cells. However, dysfunction of mitochondria is related to a variety of pathological processes and diseases. MicroRNAs (miRNAs) are a class of small noncoding RNAs about 22 nucleotides long, and they can bind to the 3'-untranslated region (3'-UTR) of mRNAs, thereby inhibiting mRNA translation or promoting mRNA degradation. We summarize the molecular regulation of mitochondrial metabolism, structure, and function by miRNAs. Modulation of miRNAs levels may provide a new therapeutic approach for the treatment of mitochondria-related diseases.