HKT1;1 and HKT1;2 Na+ transporters from Solanum galapagense play different roles in the plant Na+ distribution under salinity

Salt tolerance is a target trait in plant science and tomato breeding programs. Wild tomato accessions have been often explored for this purpose. Since shoot Na/K is a key component of salt tolerance, RNAi-mediated knockdown isogenic lines obtained for Solanum galapagense alleles encoding both class I Na transporters HKT1;1 and HKT1;2 were used to investigate the silencing effects on the Na and K contents of the xylem sap, and source and sink organs of the scion, and their contribution to salt tolerance in all 16 rootstock/scion combinations of non-silenced and silenced lines, under two salinity treatments. The results show that SgHKT1;1 is operating differently from SgHKT1;2 regarding Na circulation in the tomato vascular system under salinity. A model was built to show that using silenced SgHKT1;1 line as rootstock would improve salt tolerance and fruit quality of varieties carrying the wild type SgHKT1;2 allele. Moreover, this increasing effect on both yield and fruit soluble solids content of silencing SgHKT1;1 could explain that a low expressing HKT1;1 variant was fixed in S. lycopersicum during domestication, and the paradox of increasing agronomic salt tolerance through silencing the HKT1;1 allele from S. galapagense, a salt adapted species.

The study was funded by the Spanish Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación, grants AGL2017-82452-C2-1R (A.B.) and AGL2017-82452-C2-2R (M.J.A) both from the, MCIN/AEI/10.13039/501100011033, the European Union (H2020 SFS-28-2020), contract number 101000716 (HARNESSTOM), and FEDER “Una manera de hacer Europa”. J.E. was supported by a JAE Intro-CSIC grant, JAEINT_19_00566.