Characterization of the PaHAK Gene and Its Expression During the In Vitro Seed Germination of Two Botanical Avocado Varieties Under Saline Stress

Soil salinity is one of the main challenges that modern agriculture faces. Avocado, which is classified as a glycophyte, is very sensitive to salt stress. There are botanical varieties of avocado that differ in their salt tolerance. This study investigated how salt stress affects the in vitro germination of two avocado botanical varieties americana (West Indian breed) and drymifolia (Mexican native) with different salt tolerances. This study also assessed the potential role of the avocado <i>PaHAK2</i> high-affinity K⁺ transporter HAK/KUP/KT in response to saline stress during germination. Salinity (60 mM NaCl) delayed the germination speed of the drymifolia variety relative to the americana variety. A computational 3D inference protein model of the <i>PaHAK2</i> protein showed 10 highly conserved transmembrane domains. During the imbibition period, there was a differential increase in the expression of the <i>PaHAK2</i> gene at 60 mM NaCl in both varieties, which suggests the presence of osmotic adjustment and regulation. The enhanced expression of <i>PaHAK2</i> in the americana variety suggests an adaptive advantage to salinity. We conclude that <i>PaHAK2</i> participates in the response of avocado to salt stress during seed germination.