Genome-wide identification, evolution, and expression analysis of the KT/HAK/KUP family in pear.

The K+ transporter/high-affinity K+/K+ uptake (KT/HAK/KUP) family, as one of the largest K+ transporter families in higher plants, plays an essential role in plant growth, mineral element absorption, salt stress tolerance, and other physiological processes. However, little is known about this family in pear (Pyrus). Here, we identified 20 K+ transporter genes in pear (P. bretschneideri) using genome-wide analysis. Their gene structure, chromosomal distribution, conserved motifs, phylogenetics, duplication events, and expression patterns were also examined. The results of phylogenetic analysis showed that PbrKT/HAK/KUP genes were clustered into three major groups (Groups I-III). Among the 20 PbrKT/HAK/KUP genes, 18 were mapped to nine chromosomes and two to scaffolds. Four WGD/segmental gene pairs were identified, indicating that WGD/segmental duplication may have contributed to the expansion of the KT/HAK/KUP family in pear. Among the four pairs of WGD/segmentally duplicated genes, both members of three pairs had been subjected to purifying selection, whereas the fourth pair had been subjected to positive selection. Furthermore, phenotypic experiments showed that the growth of pear seedlings was affected by potassium deficiency treatment. Expression patterns of 20 PbrKT/HAK/KUP genes in roots were further assayed with qRT-PCR. PbrHAK1 and PbrHAK12/16 were significantly expressed in response to K+ deficiency, suggesting that these genes are crucial for K+ uptake in pear, especially under the condition of K+ starvation. Our results provide a foundation for further study on the function of KT/HAK/KUP genes in pear.