Phylogenetic and Expression Analysis of Mn-CDF Transporters in Pear (Pyrus bretschneideri Rehd.)

Metal tolerance proteins (MTPs) play important roles in heavy metal homeostasis and tolerance in plants. As a part of the MTP family, manganese-cation diffusion facilitator (Mn-CDF) subfamily members transport Mn and iron (Fe) in plants. However, the role of these Mn-CDFs in pear is not well established. In this study, seven members of the Mn-CDF subgroup were identified in Chinese white pear (Pyrus bretschneideri Rehd.), based on recently released draft genome of pear. These members were predicted to encode proteins ranging from 394 to 416 amino acids, including 6 putative transmembrane domains (TMDs), and predicted to localize in the Golgi or vacuole membrane. Furthermore, all the members contained a highly conserved signature sequence in TMD-II and TMD-V. Yeast functional complementation assays demonstrated that the expression of PbMTP8.1, PbMTP8.2, PbMTP9, and PbMTP10 in particular conferred Mn and Fe tolerance, while PbMTP11.1 and PbMTP11.2 only transport Mn, and PbMTP11.3 transports neither Mn nor any other ion that was used in the study. Quantitative real-time PCR analysis indicated that these genes were widely expressed in the root, stem, and leaf tissues of the pear seedlings, but the expression levels differed among the different tissues. The results provide us with systematic information about the Mn-CDF subgroup genes and their possible roles in the distribution and homeostasis of Mn and Fe in pear.