The mitogen-activated protein kinase (MAPK) cascade is a highly conserved signaling transduction module that transduces extracellular stimuli into intracellular responses in plants. Early studies of plant MAPKs focused on their functions in model plants. Based on the results of whole-genome sequencing, many MAPKs have been identified in horticultural plants, such as tomato and apple. Recent studies revealed that the MAPK cascade also plays crucial roles in the biotic and abiotic stress responses of horticultural plants. In this review, we summarize the composition and classification of MAPK cascades in horticultural plants and recent research on this cascade in responses to abiotic stresses (such as drought, extreme temperature and high salinity) and biotic stresses (such as pathogen infection). In addition, we discuss the most advanced research themes related to plant MAPK cascades, thus facilitating research on MAPK cascade functions in horticultural plants.

Apple (malus domestica Borkh.), which is a widely cultivated, important and economic fruit crop with nutritive and medicinal importance, has emerged as a model horticultural crop in this post-genomic era. Wild apple resources are important and they develop gradually in apple industry and genetic diversity. In this study, two molecular markers (inter-simple sequence repeats, ISSR and sequence-specific amplification polymorphism, S-SAP) were evaluated for genetic analysis of 31 wild apple resources in Shandong. A total of 20 ISSR primers were used and 110 polymorphic bands were amplified. Five S-SAP primer sets yielded a total of 496 bands, of which 201 (40.52%) were polymorphic. The similarity coefficient between resources ranged from 0.70 to 0.94 for ISSR analysis and from 0.66 to 0.95 using the S-SAP methodology. This study indicates that the results obtained based on the dendrograms constructed using unweighted pair-group using arithmetic average (UPGMA) cluster analysis were significantly correlated. The ISSR and S-SAP markers were found to be useful for wild apple resources identification and assessment of phonetic relationships. Key words: Apple, wild resource, inter-simple sequence repeats (ISSR), sequence-specific amplification polymorphism (S-SAP).