Molecular characterization and phylogenetic analysis of ZmMCUs in maize

The mitochondrial calcium uniporter (MCU), located in the organelle’s inner membrane of eukaryotic organisms, is a highly selective ion channel which plays a unique role in the calcium signaling. Six MCU-like genes (assigned as ZmMCU1∼ZmMCU6) were identified in the maize genome. Genomic analysis revealed that these six genes were located on chromosome 1, 3, 8 and 9. Sequence identity percent between ZmMCU1 and ZmMCU2, or between ZmMCU4 and ZmMCU5 was relatively high at both the nucleic acid and amino acid levels. Sequence alignment of ZmMCU indicated that for plants, there was “DVME” motif in the deduced protein sequences. Digital expression analysis showed the ZmMCU6 was strongly expressed in all of the studied organs in maize, while the other five ZmMCU genes had unique expression patterns. In the developing seeds of maize, the six ZmMCU genes had three divergent expression patterns. Finally, the phylogenetic analysis demonstrated that MCU homologs in plants could be grouped into two types and each type could be further classified into two subtypes along the monocot and dicot division. Moreover, MCU homologs in both the dicot and monocot had been independently duplicated and then those in maize had undergone an extra duplication for two subclades. Based on genomic structure, sequence similarity, digital expression profile, and phylogenetic analysis, our results clearly suggested that ZmMCU1 and ZmMCU2 as well as ZmMCU4 and ZmMCU5 are functionally redundant in maize genome.