Genome-wide identification, characterization and expression analysis of HAK genes and decoding their role in responding to potassium deficiency and abiotic stress in Medicago truncatula

Background: The HAK family is the largest potassium (K+) transporter family, vital in K+ uptake, plant growth, and both plant biotic and abiotic stress responses. Although HAK family members have been characterized and functionally investigated in many species, these genes are still not studied in detail in Medicago truncatula, a good model system for studying legume genetics. Methods: In this study, we screened the M. truncatula HAK family members (MtHAKs). Furthermore, we also conducted the identification, phylogenetic analysis, and prediction of conserved motifs of MtHAKs. Moreover, we studied the expression levels of MtHAKs under K+ deficiency, drought, and salt stresses using quantitative real-time PCR (qRT-PCR). Results: We identified 20 MtHAK family members and classified them into three clusters based on phylogenetic relationships. Conserved motif analyses showed that all MtHAK proteins besides MtHAK10 contained the highly conserved K+ transport domain (GVVYGDLGTSPLY). qRT-PCR analysis showed that several MtHAK genes in roots were induced by abiotic stress. In particular, MtHAK15, MtHAK17, and MtHAK18 were strongly up-regulated in the M. truncatula roots under K+ deficiency, drought, and salt stress conditions, thereby implying that these genes are good candidates for high-affinity K+ uptake and therefore have essential roles in drought and salt tolerance. Discussions: Our results not only provided the first genetic description and evolutionary relationships of the K+ transporter family in M. truncatula, but also the potential information responding to K+ deficiency and abiotic stresses, thereby laying the foundation for molecular breeding of stress-resistant legume crops in the future.