Na+ transporter HKT1;2 reduces flower Na+ content and considerably mitigates the decline in tomato fruit yields under saline conditions

Abstract

Genes encoding HKT1-like Na⁺ transporters play a key role in the salinity tolerance mechanism in Arabidopsis and other plant species by retrieving Na⁺ from the xylem of different organs and tissues. In this study, we investigated the role of two HKT1;2 allelic variants in tomato salt tolerance in relation to vegetative growth and fruit yield in plants subjected to salt treatment in a commercial greenhouse under real production conditions. We used two near-isogenic lines (NILs), homozygous for either the Solanum lycopersicum (NIL17) or S. cheesmaniae (NIL14) allele, at HKT1;2 loci and their respective RNAi-Sl/ScHKT1;2 lines. The results obtained show that both ScHKT1;2- and SlHKT1;2-silenced lines display hypersensitivity to salinity associated with an altered leaf Na⁺/K⁺ ratio, thus confirming that HKT1;2 plays an important role in Na⁺ homeostasis and salinity tolerance in tomato. Both silenced lines also showed Na⁺ over-accumulation and a slight, but significant, reduction in K⁺ content in the flower tissues of salt-treated plants and consequently a higher Na⁺/K⁺ ratio as compared to the respective unsilenced lines. This altered Na⁺/K⁺ ratio in flower tissues is associated with a sharp reduction in fruit yield, measured as total fresh weight and number of fruits, in both silenced lines under salinity conditions. Our findings demonstrate that Na⁺ transporter HKT1;2 protects the flower against Na⁺ toxicity and mitigates the reduction in tomato fruit yield under salinity conditions.

Keywords: Fruit yield; HKT1;2 gene; K(+) and Na(+) homeostasis; Na(+) flower content; Salinity; Solanum lycopersicum and S. cheesmaniae; Tomato.