RESUMEN
Peel degreening is the most conspicuous aspect of fruit ripening in many citrus fruits because of its importance for marketability. In this study, peel degreening in response to propylene (an ethylene analog) and at varying storage temperatures was characterized in Satsuma mandarin (Citrus unshiu Marc.) fruit. Propylene treatment triggered rapid peel degreening (within 4-6 days), indicated by an increase in the citrus color index (CCI) and chlorophyll loss. Peel degreening was also observed in fruit at 10°C and 15°C after 28-42 days, with gradual CCI increase and chlorophyll reduction. However, fruit at 5°C, 20°C, and 25°C remained green, and no substantial changes in peel CCI and chlorophyll content were recorded during the 42-day storage duration. The transcriptomes of peels of fruit treated with propylene for 4 days and those stored at varying temperatures for 28 days were then analyzed by RNA-Seq. We identified three categories of differentially expressed genes that were regulated by (i) propylene (and by analogy, ethylene) alone, (ii) low temperature (5°C, 10°C, or 15°C vs. 25°C) alone, and (iii) either propylene or low temperature. Gene-encoding proteins associated with chlorophyll degradation (such as CuSGR1, CuNOL, CuACD2, CuCAB2, and CuLHCB2) and a transcription factor (CuERF114) were differentially expressed by propylene or low temperature. To further examine temperature-induced pathways, we also monitored gene expression during on-tree fruit maturation vs. postharvest. The onset of on-tree peel degreening coincided with autumnal drops in field temperatures, and it was accompanied by differential expression of low temperature-regulated genes. On the contrary, genes that were exclusively regulated by propylene (such as CuCOPT1 and CuPOX-A2) displayed insignificant expression changes during on-tree peel degreening. These findings indicate that low temperatures could be involved in the fruit ripening-related peel degreening independently of ethylene.
RESUMEN
The complete genomic RNAs of two Korean sacbrood virus (SBV) strains, which infect the honey bee, Apis mellifera, were sequenced. The two sequences (AmSBV-Kor19, AmSBV-Kor21) were distinguished by the presence or absence of a PstI restriction site. These strains comprised of 8784 bp and 8835 bp; contained a single large ORF (179-8707 and 179-8758) encoding 2843 and 2860 amino acids, respectively. Deduced amino acid sequences comparison with some insect viruses showed that regions of helicase, protease and RdRp domains; structural genes were located at the 5' end and non-structural genes at the 3' end. Multiple sequence alignment showed that AmSBV-Kor19 was missing a section between nucleotides 2311 and 2361 (present in SBV-UK and CSBV) but was similar to that of the Korean SBV strain that infects A. cerana (AcSBV-Kor). The differences in the AmSBV-Kor19 strain may be the result of the virus adapting to a different host.