Genome wide identification and functional analyses of HAK family potassium transporter genes in passion fruit (Passiflora edulis Sims) in response to potassium deficiency and stress responses

The nutritional status of potassium directly affects the yield and quality of fruits. The molecular mechanism underlying K⁺ uptake and transport in passion fruit (Passiflora edulis Sims), particularly under K⁺ limited conditions, remains poorly understood. Members of the high-affinity K⁺ (HAK) transporter family play a vital role in K⁺ acquisition, translocation, and stress responses. However, the biological functions of these genes in passion fruit plants are still unknown. This study identified 14 HAK genes (PeHAKs) in Passiflora edulis genome. Phylogenetic analysis classified these PeHAKs into three distinct clusters containing 9, 4, and 1 genes, respectively, with conserved structural features supporting their functional divergence. Promoter analysis revealed 12 predominant cis-acting elements, including hormone-responsive, stress-inducible, and core transcriptional regulatory motifs. Tissue-specific expression profiling demonstrated significant organ-dependent expression patterns of PeHAKs across roots, stems, leaves (young/mature), flowers, and fruits. Under K⁺ deficiency, salinity stress, and phytohormone treatments, the transcript levels of PeHAKs were significantly altered in roots and leaves. Notably, PeHAK10 exhibited dual induction in aerial and subterranean tissues under K⁺ deprivation. Functional complementation assays in yeast validated the K⁺/Na ⁺ transport activity of PeHAK10, suggesting its involvement in ion homeostasis regulation during nutrient stress. This study provides the first genome-wide characterization of the PeHAKs family of genes in passion fruit plants, establishing a foundation for elucidating their biological roles in potassium nutrition regulation and stress adaptation.