Variation in TaSPL6-D confers salinity tolerance in bread wheat by activating TaHKT1;5-D while preserving yield-related traits

Abstract

Na⁺ exclusion from above-ground tissues via the Na⁺-selective transporter HKT1;5 is a major salt-tolerance mechanism in crops. Using the expression genome-wide association study and yeast-one-hybrid screening, we identified TaSPL6-D, a transcriptional suppressor of TaHKT1;5-D in bread wheat. SPL6 also targeted HKT1;5 in rice and Brachypodium. A 47-bp insertion in the first exon of TaSPL6-D resulted in a truncated peptide, TaSPL6-D^In, disrupting TaHKT1;5-D repression exhibited by TaSPL6-D^Del. Overexpressing TaSPL6-D^Del, but not TaSPL6-D^In, led to inhibited TaHKT1;5-D expression and increased salt sensitivity. Knockout of TaSPL6-D^Del in two wheat genotypes enhanced salinity tolerance, which was attenuated by a further TaHKT1;5-D knockdown. Spike development was preserved in Taspl6-dd mutants but not in Taspl6-aabbdd mutants. TaSPL6-D^In was mainly present in landraces, and molecular-assisted introduction of TaSPL6-D^In from a landrace into a leading wheat cultivar successfully improved yield on saline soils. The SPL6-HKT1;5 module offers a target for the molecular breeding of salt-tolerant crops.