The Siberian wild apple, Malus baccata (L.) Borkh., is an additional contributor to the genomes of cultivated European and Chinese apples

It is crucial to understand domestication to unravel the evolutionary processes that shape the divergence of populations. Differences in life-history traits have probably led to marked differences in the mode and speed of evolution between trees and annuals, particularly the extent of crop-wild gene flow during domestication. Apple is an iconic tree and major fruit crop grown worldwide. The contribution of wild apple species to the genetic makeup of the cultivated apple genome remains a topic of intense investigations. We used population genomics in combination with SNPs to investigate the contributions of the two known wild apple relatives, Malus sylvestris and Malus sieversii, and a supposed contributor, Malus baccata, to European and Chinese rootstock and dessert genomes, with a focus on the extent of wild-crop gene flow during apple domestication. We showed that the European dessert and rootstock apples form a specific gene pool, whereas the Chinese dessert and rootstock apples were a mixture of three wild gene pools. Coalescent-based inferences and gene flow estimates indicated that M. baccata is an additional contributor to the genome of both European and Chinese cultivated apples through wild-to-crop introgressions. We also confirmed previous results on the contribution of M. sylvestris to the cultivated apple genome, and provided insights into the origin of the apple rootstock. This study further demonstrates the role of gene flow during apple domestication, as seen in other woody perennials, and show that domestication of the apple tree involved several wild apple species.

Genome-wide identification, characterization and expression analysis of MATE family genes in apple (Malus × domestica Borkh)

Background As an important group of the multidrug efflux transporter family, the multidrug and toxic compound extrusion (MATE) family has a wide range of functions and is distributed in all kingdoms of living organisms. However, only two MATE genes in apple have been analyzed and genome-wide comprehensive analysis of MATE family is needed. Results In this study, a total of 66 MATE (MdMATE) candidates encoding putative MATE transporters were identified in the apple genome. These MdMATE genes were classified into four groups by phylogenetic analysis with MATE genes in Arabidopsis. Synteny analysis reveals that whole genome duplication (WGD) and segmental duplication events played a major role in the expansion of MATE gene family in apple. MdMATE genes show diverse expression patterns in different tissues/organs and developmental stages. Analysis of cis-regulatory elements in MdMATE promoter regions indicates that the function of MdMATE genes is mainly related to stress response. Besides, the changes of gene expression levels upon different pathogen infections reveal that MdMATE genes are involved in biotic stress response. Conclusions In this work, we systematically identified MdMATE genes in apple genome using a set of bioinformatics approaches. Our comprehensive analysis provided valuable resources for improving disease resistance in apple and further functional characterization of MATE genes in other species.

Genome-Wide Identification of PRP Genes in Apple Genome and the Role of MdPRP6 in Response to Heat Stress

Plant proline-rich proteins (PRPs) are cell wall proteins that occur in the plant kingdom and are involved in plant development and stress response. In this study, 9 PRP genes were identified from the apple genome and a comprehensive analysis of the PRP family was conducted, including gene structures, phylogenetic analysis, chromosome mapping, and so on. The expression of MdPRPs varied among tissues and in response to different types of stresses. MdPRP4 and MdPRP7 were induced by five detected stress treatments, including heat, drought, abscisic acid, cold, and salt; the expression patterns of the others varied under different types of stress. Subcellular localization showed that MdPRPs mainly functioned in the cytoplasm, except for MdPRP1 and MdPRP5, which also functioned in the nucleus. When MdPRP6 was overexpressed in tobacco, the transgenic plants showed higher tolerance to high temperature (48 °C) compared with wild-type (WT) plants. The transgenic plants showed milder wilting, a lower accumulation of electrolyte leakage, MDA and ROS, and a higher level of chlorophyll and SOD and POD activity, indicating that MdPRP6 may be an important gene in apples for heat stress tolerance. Overall, this study suggested that MdPRPs are critically important for the ability of apple responses to stresses.

Structural and functional apple genomics and its application in breeding

The present paper summarized some knowledge of modern technologies, applied in apple (Malus domestica) genome studies. New generation sequencing allowed single nucleotide polymorphism (SNP) chip technologies for genotyping, description of functional apple genes, characterization of the evolutionary results in apple genome fragment transition, as well as phylogenetic reconstruction of the genus Malus, being the confirmed progeny of M. sieviersii. Based on these technologies, newly developed putative markers may give the most important biological data such as age, geographical origins, tissue type determination, and external visible characters. The new generation genotyping platforms, representing very high efficiency, are now successfully applied for random apple genome-wide association (GWA) studies as well pedigree-based analysis and marker-assisted selection (MAS).