Linking Duplication of a Calcium Sensor to Salt Tolerance in .

The SALT-OVERLY-SENSITIVE (SOS) pathway in Arabidopsis () functions to prevent the toxic accumulation of sodium in the cytosol when plants are grown in salt-affected soils. In this pathway, the CALCINEURIN B-LIKE10 (AtCBL10) calcium sensor interacts with the AtSOS2 kinase to activate the AtSOS1 plasma membrane sodium/proton exchanger. has been duplicated in Eutrema (), a salt-tolerant relative of Arabidopsis. Because Eutrema maintains growth in salt-affected soils that kill most crop plants, the duplication of provides a unique opportunity to functionally test the outcome of gene duplication and its link to plant salt tolerance. In Eutrema, individual down-regulation of the duplicated genes ( and ) decreased growth in the presence of salt and, in combination, led to an even greater decrease, suggesting that both genes function in response to salt and have distinct functions. Cross-species complementation assays demonstrated that has an enhanced ability to activate the SOS pathway while has a function not performed by or Chimeric EsCBL10a/EsCBL10b proteins revealed that the specific functions of the EsCBL10 proteins resulted from changes in the amino terminus. The duplication of increased calcium-mediated signaling capacity in Eutrema and conferred increased salt tolerance to salt-sensitive Arabidopsis.