Red coloration of fruit is an important trait in apple, and it is mainly attributed to the accumulation of anthocyanins, a class of plant flavonoid metabolites. Anthocyanin biosynthesis is genetically determined by structural and regulatory genes. Plant tissue pigmentation patterns are mainly controlled by expression profiles of regulatory genes. Among these regulatory genes are MYB transcription factors (TFs), wherein the class of two-repeats (R2R3) is deemed the largest, and these are associated with the anthocyanin biosynthesis pathway. Although three MdMYB genes, almost identical in nucleotide sequences, have been identified in apple, it is likely that there are other R2R3 MYB TFs that are present in the apple genome that are also involved in the regulation of coloration of red color pigmentation of the skin of apple fruits.

Three genes encoding flavonoid 3′-hydroxylase (F3′H) in apple (Malus × domestica), designated MdF3′HI, MdF3′HIIa, and MdF3′HIIb, have been identified. MdF3′HIIa and MdF3′HIIb are almost identical in amino acid sequences, and they are allelic, whereas MdF3′HI has 91% nucleotide sequence identity in the coding region to both MdF3′HIIa and MdF3′HIIb. MdF3′HI and MdF3′HII genes are mapped onto linkage groups 14 and 6, respectively, of the apple genome. Throughout the development of apple fruit, transcriptional levels of MdF3′H genes along with other anthocyanin biosynthesis genes are higher in the red-skinned cv Red Delicious than that in the yellow-skinned cv Golden Delicious. Moreover, patterns of MdF3′H gene expression correspond to accumulation patterns of flavonoids in apple fruit. These findings suggest that MdF3′H genes are coordinately expressed with other genes in the anthocyanin biosynthetic pathway in apple. The functionality of these apple F3′H genes has been demonstrated via their ectopic expression in both the Arabidopsis (Arabidopsis thaliana) transparent testa7-1 (tt7) mutant and tobacco (Nicotiana tabacum). When grown under nitrogen-deficient conditions, transgenic Arabidopsis tt7 seedlings expressing apple F3′H regained red color pigmentation and significantly accumulated both 4′-hydrylated pelargonidin and 3′,4′-hydrylated cyanidin. When compared with wild-type plants, flowers of transgenic tobacco lines overexpressing apple F3′H genes exhibited enhanced red color pigmentation. This suggests that the F3′H enzyme may coordinately interact with other flavonoid enzymes in the anthocyanin biosynthesis pathway.

Association mapping (AM), also known as linkage disequilibrium (LD) mapping, is a viable approach to overcome limitations of pedigree-based quantitative trait loci (QTL) mapping. In AM, genotypic and phenotypic correlations are investigated in unrelated individuals. Unlike QTL mapping, AM takes advantage of both LD and historical recombination present within the gene pool of an organism, thus utilizing a broader reference population. In plants, AM has been used in model species with available genomic resources. Pursuing AM in tree species requires both genotyping and phenotyping of large populations with unique architectures. Recently, genome sequences and genomic resources for forest and fruit crops have become available. Due to abundance of single nucleotide polymorphisms (SNPs) within a genome, along with availability of high-throughput resequencing methods, SNPs can be effectively used for genotyping trees. In addition to DNA polymorphisms, copy number variations (CNVs) in the form of deletions, duplications, and insertions also play major roles in control of expression of phenotypic traits. Thus, CNVs could provide yet another valuable resource, beyond those of microsatellite and SNP variations, for pursuing genomic studies. As genome-wide SNP data are generated from high-throughput sequencing efforts, these could be readily reanalysed to identify CNVs, and subsequently used for AM studies. However, forest and fruit crops possess unique architectural and biological features that ought to be taken into consideration when collecting genotyping and phenotyping data, as these will also dictate which AM strategies should be pursued. These unique features as well as their impact on undertaking AM studies are outlined and discussed.

Three genes encoding anthocyanidin reductase (ANR) in apple (Malus×domestica Borkh.), designated MdANR1, MdANR2a, and MdANR2b, have been cloned and characterized. MdANR1 shows 91% identity in coding DNA sequences with MdANR2a and MdANR2b, while MdANR2a and MdANR2b are allelic and share 99% nucleotide sequence identity in the coding region. MdANR1 and MdANR2 genes are located on linkage groups 10 and 5, respectively. Expression levels of both MdANR1 and MdANR2 genes are generally higher in yellow-skinned cv. Golden Delicious than in red-skinned cv. Red Delicious. Transcript accumulation of MdANR1 and MdANR2 genes in fruits gradually decreased throughout fruit development. Ectopic expression of apple MdANR genes in tobacco positively and negatively regulates the biosynthesis of proanthocyanidins (PAs) and anthocyanin, respectively, resulting in white, pale pink-coloured, and white/red variegated flowers. The accumulation of anthocyanin is significantly reduced in all tobacco transgenic flowers, while catechin and epicatechin contents in transgenic flowers are significantly higher than those in flowers of wild-type plants. The inhibition of anthocyanin synthesis in tobacco transgenic flowers overexpressing MdANR genes is probably attributed to down-regulation of CHALCONE ISOMERASE (CHI) and DIHYDROFLAVONOL-4-REDUCTASE (DFR) genes involved in the anthocyanin pathway. Interestingly, several transgenic lines show no detectable transcripts of the gene encoding leucoanthocyanidin reductase (LAR) in flowers, but accumulate higher levels of catechin in flowers of transgenic plants than those of wild-type plants. This finding suggests that the ANR gene may be capable of generating catechin via an alternative route, although this mechanism is yet to be further elucidated.

Two-component signal transduction systems (TCSTs), consisting of a histidine kinase (HK) and a response regulator (RR), represent a major paradigm for signal transduction in prokaryotes. TCSTs play critical roles in sensing and responding to environmental conditions, and in bacterial pathogenesis. Most TCSTs in Erwinia amylovora have either not been identified or have not yet been studied.

Considering the complexity of the current framework in oncology, the relevance of animal models in biomedical research is critical in light of the capacity to produce valuable data with clinical translation. The laboratory mouse is the most common animal model used in cancer research due to its high adaptation to different environments, genetic variability, and physiological similarities with humans. Beginning with spontaneous mutations arising in mice colonies that allow for pursuing studies of specific pathological conditions, this area of in vivo research has significantly evolved, now capable of generating humanized mice models encompassing the human immune system in biological correlation with human tumor xenografts. Moreover, the era of genetic engineering, especially of the hijacking CRISPR/Cas9 technique, offers powerful tools in designing and developing various mouse strains. Within this article, we will cover the principal mouse models used in oncology research, beginning with behavioral science of animals vs. humans, and continuing on with genetically engineered mice, microsurgical-induced cancer models, and avatar mouse models for personalized cancer therapy. Moreover, the area of spontaneous large animal models for cancer research will be briefly presented.