Mutation of the K+ transporter SlHAK5 of tomato alters pistil morphology, ionome, metabolome and transcriptome in flowers.

K⁺ accumulation in plant tissues is a crucial factor for plant growth and development. The tomato high-affinity K⁺ transporter SlHAK5 is essential for root K⁺ acquisition from low external concentrations. It is also involved in K⁺ accumulation in pollen and plant fertility as slhak5 KO plants show a low rate of pollen germination, impaired pollen tube growth and parthenocarpic fruits. Here, we present a thorough analysis of slhak5 flowers, which showed relevant defects at the anatomic, ionomic, metabolomic and transcriptomic levels. First, slhak5 flowers exhibited shorter styles and enlarged ovaries that, together with a low number of seeds in fruits from slhak5 X WT crosses, indicated an effect of the slhak5 mutation on female fertility. Second, a lower accumulation of Ca²⁺, as well as of several metabolites such as amino acids, citric acid and sugars, was observed in mutant flowers, whereas indole-3-acetic acid content was increased when compared to the wild-type. Third, RNAseq conducted on pistils and stamens of wild-type and slhak5 plants revealed that transport and signalling pathways are significantly enriched in the gene expression analyses of stamens. Thus, it can be concluded that a functional SlHAK5 transporter is required to maintain appropriate Ca²⁺, metabolite and gene expression levels in flowers, and its absence leads to important reductions in both male and female fertility.