Genome-wide identification and analysis of MICU genes in land plants and their potential role in calcium stress

Mitochondrial calcium uptake (MICU) plays a vital role in the regulation of mitochondrial calcium homeostasis, and, consequently, influences calcium signaling transduction. Although genes involved in mitochondrial calcium uptake have been well studied in animals, less is known about their ubiquity and function in plants. In this study, we identified 96 MICU genes in land plants. On the basis of phylogenetic analysis of MICU proteins, they were classified into three clades: MICU from eudicots (Clade I), from monocots (Clade II), and from a basal angiosperm, a bryophyte, and a lycophyte (Clade III). Pairwise identity analysis across all MICU proteins showed that they are highly conserved among land plants at the protein level. Conserved motif analysis showed that most MICU proteins contained three EF-hands, and an additional EF-hand motif first identified in the MICU of Arabidopsis thaliana but not mammals was found in all 96 putative MICU proteins. This suggests that a cellular pathway of calcium uptake and signaling that requires three EF-hand motifs is evolutionarily conserved in plants. In addition, we discovered that MICU-defective mutants of Arabidopsis thaliana exhibited longer roots than wild-type under high calcium stress. Concurrently, the mRNA transcription levels of MICU were decreased under high calcium conditions. These results suggest that loss-of-function mutations of MICU may have potential roles in helping plants resist high calcium stress. This study provides clues to the possible role of plant MICU in mitochondrial calcium uptake, as well as useful information to support further studies on MICU function in plants.