LbKAT3 may assist in mycorrhizal potassium uptake, and overexpression of LbKAT3 may promote potassium, phosphorus, and water transport from arbuscular mycorrhizal fungi to the host plant

Abstract

Potassium plays important roles in most plant physiological processes. Arbuscular mycorrhizal (AM) fungi promote plant water and mineral nutrient acquisition to promote plant growth. However, few studies have focused on the effect of AM colonization on potassium uptake by the host plant. In this study, the effects of an AM fungus (<i>Rhizophagus irregularis</i>) and potassium concentration (0, 3, or 10 mM K⁺) on <i>Lycium barbarum</i> were evaluated. A split-root test with <i>L. barbarum</i> seedlings was conducted, and the potassium uptake capacity of LbKAT3 was verified in yeast. A tobacco line overexpressing <i>LbKAT3</i> was generated and mycorrhizal functions under two potassium concentrations (0.2 and 2 mM K⁺) were studied. Inoculation of <i>R. irregularis</i> and application of potassium increased the dry weight, and potassium and phosphorus contents of <i>L. barbarum</i>, and increased the colonization rate and arbuscule abundance of <i>R. irregularis</i>. In addition, the expression of <i>LbKAT3</i> and <i>AQP</i> genes in <i>L. barbarum</i> was upregulated. Inoculation of <i>R. irregularis</i> induced <i>LbPT4</i>, <i>Rir-AQP1</i>, and <i>Rir-AQP2</i> expression, and application of potassium upregulated the expression of these genes. Inoculation with the AM fungus locally regulated the expression of <i>LbKAT3</i>. Inoculation of <i>R. irregularis</i> improved the growth, and potassium and phosphorus contents, and induced <i>NtPT4</i>, <i>Rir-AQP1</i>, and <i>Rir-AQP2</i> expression in tobacco overexpressing <i>LbKAT3</i> under both potassium concentrations. Overexpression of <i>LbKAT3</i> in tobacco improved the growth, potassium accumulation, and AM colonization, and upregulated the expression of <i>NtPT4</i> and <i>Rir-AQP1</i> in mycorrhizal tobacco. The results suggest that <i>LbKAT3</i> may assist in mycorrhizal potassium uptake, and overexpression of <i>LbKAT3</i> may promote potassium, phosphorus, and water transport from the AM fungus to tobacco.