A novel function of the tomato CALCINEURIN-B LIKE 10 gene as a root-located negative regulator of salt stress.

Climate change exacerbates abiotic stresses like salinization, negatively impacting crop yield, so development of strategies, like using salt-tolerant rootstocks, is crucial. The CALCINEURIN B-LIKE 10 (SlCBL10) gene has been previously identified as a positive regulator of salt tolerance in the tomato shoot. Here, we report a different function of SlCBL10 in tomato shoot and root, as disruption of SlCBL10 only induced salt sensitivity when it was used in the scion but not in the rootstock. The use of SlCBL10 silencing rootstocks (Slcbl10 mutant and RNAi line) improved salt tolerance on the basis of fruit yield. These changes were associated with improved Na and K homoeostasis, as SlCBL10 silencing reduced the Na content and increased the K content under salinity, not only in the rootstock but also in the shoot. Improvement of Na homoeostasis in Slcbl10 rootstock seems to be mainly due to induction of SlSOS1 expression, while the higher K accumulation in roots seems to be mainly determined by expression of LKT1 transporter and SlSKOR channel. These findings demonstrate that SlCBL10 is a negative regulator of salt tolerance in the root, so the use of downregulated SlCBL10 rootstocks may provide a suitable strategy to increase tomato fruit production under salinity.