Duplication and functional divergence of a calcium sensor in the Brassicaceae

The presence of varied numbers of CALCINEURIN B-LIKE10 (CBL10) calcium sensor genes in species across the Brassicaceae and the demonstrated role of CBL10 in salt tolerance in Arabidopsis thaliana and Eutrema salsugineum provided a unique opportunity to determine if CBL10 function is modified in different species and linked to salt tolerance. Salinity effects on species growth and cross-species complementation were used to determine the extent of conservation and divergence of CBL10 function in four species representing major lineages within the core Brassicaceae (A. thaliana, E. salsugineum, Schrenkiella parvula, and Sisymbrium irio) as well as the first diverging lineage (Aethionema arabicum). Evolutionary and functional analyses indicate that CBL10 duplicated within expanded lineage II of the Brassicaceae and that, while portions of CBL10 function are conserved across the family, there are species-specific variations in CBL10 function. Paralogous CBL10 genes within a species diverged in expression and function probably contributing to the maintenance of the duplicated gene pairs. Orthologous CBL10 genes diverged in function in a species-specific manner, suggesting that functions arose post-speciation. Multiple CBL10 genes and their functional divergence may have expanded calcium-mediated signaling responses and contributed to the ability of certain members of the Brassicaceae to maintain growth in salt-affected soils.