A potassium (K)-transporter, OsHAK3, is required for K- homeostasis in rice under low-K and high-salinity conditions

Potassium (K+) is a macronutrient for plant growth and development. Although a number of K-transporters are encoded in various plant genomes, functional characterization of these transport genes have lagged behind of genomic information in crop plants. In rice genome, a large expansion of high-affinity K-transporters (HAKs/KUPs/KTs) has been identified as compared to those in Arabidopsis genome suggesting a functional diversity of these transporters in cereals. We report here the functional characterization of a HAK member, OsHAK3, in rice using CRISPR-assisted genetic analysis. Expression of OsHAK3 was mainly found in roots and its protein was targeted to the plasma membrane. Loss of function of OsHAK3 led to a reduction of K+ uptake rate and K+ content, consistent with the finding that mutant plants became stunted under low-K+ conditions. In addition, the growth of Oshak3 mutants was more sensitive to salt stress due to altered K/Na ratio in the plants. Together, our data demonstrate that OsHAK3 plays a crucial role in K+ homeostasis, especially under K+-limited conditions and when plants face salinity stress.