Genome-Wide analysis of aluminum-activated malate transporter family genes in six rosaceae species, and expression analysis and functional characterization on malate accumulation in Chinese white pear

Aluminum-activated malate transporters (ALMTs) exhibit a variety of physiological roles in plants to regulate fruit quality, but the evolutionary history of the ALMT family in the Rosaceae species remains unknown. In this study, a total of 113 ALMT homologous genes were identified from six Rosaceae species (Pyrus bretschneideri, Malus × domestica, Prunus persica, Fragaria vesca, Prunus mume, and Pyrus communis), and 27 of these sequences came from Chinese white pear, designated PbrALMT. Based on the phylogenetic analysis, we divided these ALMT genes into three main clusters (A-C). Conserved domain analysis indicated that all PbrALMT proteins contained the ALMT domain and the FUSC_2 domain, and fewer proteins included the FUSC domain. The results of subcellular localization experiments showed that parts of PbrALMT proteins containing the FUSC domain were located in the membrane. Collinearity analysis revealed that segmental and dispersed duplications were the primary forces underlying ALMT gene family expansion in the Rosaceae. Calculation of Ka/Ks between the paralogous pairs indicated that all of the genes in the PbrALMT family have evolved under negative selection. Combining the changes of malate content and transcriptome data analysis, five genes belonging to Cluster B were chosen for qRT-PCR, and the results revealed that Pbr020270.1, as a candidate gene, may play important roles in malate accumulation during pear fruit development. Further transgenic assay confirmed the above conclusion. The present study provides a foundation to better understand the molecular evolution of ALMT genes in pear and the functional characterization of these genes in the future.