Receptor-like protein kinase BAK1 promotes K+ uptake by regulating H+-ATPase AHA2 under low potassium stress

Abstract

Potassium (K+) is one of the essential macronutrients for plant growth and development. However, the available K+ concentration in soil is relatively low. Plant roots can perceive low K+ (LK) stress, then enhance high-affinity K+ uptake by activating H+-ATPases in root cells, but the mechanisms are still unclear. Here, we identified the receptor-like protein kinase BAK1 (Brassinosteroid Insensitive 1-Associated Receptor Kinase 1) that is involved in LK response by regulating the Arabidopsis (Arabidopsis thaliana) PM (plasma membrane) H+-ATPase isoform 2 (AHA2). The bak1 mutant showed leaf chlorosis phenotype and reduced K+ content under LK conditions, which was due to the decline of K+ uptake capacity. BAK1 could directly interact with the AHA2 C terminus and phosphorylate T858 and T881, by which the H+ pump activity of AHA2 was enhanced. The bak1 aha2 double mutant also displayed a leaf chlorosis phenotype that was similar to their single mutants. The constitutively activated form AHA2Δ98 and phosphorylation-mimic form AHA2T858D or AHA2T881D could complement the LK sensitive phenotypes of both aha2 and bak1 mutants. Together, our data demonstrate that BAK1 phosphorylates AHA2 and enhances its activity, which subsequently promotes K+ uptake under LK conditions.

Light-induced stomatal opening requires phosphorylation of the C-terminal autoinhibitory domain of plasma membrane H+-ATPase

“…In this study, we discovered that Thr-881 is also phosphorylated in guard cells in both blue light- and photosynthesis-dependent manners. A recent study suggested that Thr-881 is phosphorylated in plants in response to low K + treatments 36 . Thus, the phosphorylation level of Thr-881 appears to be regulated as a terminal point in the signalling pathways of various external cues.…”

“…The inhibitory effect of the C-terminal domain on H + -ATPase activity is thought to be caused by two regions (regions I and II) which possibly interact and interfere with the catalytic domains 32 , 35 . The Thr-881 of AHA1 in region I is highly conserved in plants, and a recent study showed that AHA2 phosphorylation at Thr-881 is enhanced in Arabidopsis roots under low K + conditions 36 . Mutational experiments using a yeast heterologous expression system have indicated that the phosphorylation of Thr-881 increases H + -ATPase activity without affecting 14-3-3 protein binding 37 .…”

MxMPK6‐2‐mediated phosphorylation enhances the response of apple rootstocks to Fe deficiency by activating PM H+‐ATPase MxHA2

“…Numerous studies have assessed protein phosphorylation modifications of PM H + ‐ATPase. Multiple kinases, such as PSYR1, BAK1 and CDK1, phosphatases PP2A/2C, can regulate PM H + ‐ATPase activity by phosphorylating or dephosphorylating PM H + ‐ ATPase (Fuglsang et al., 2006; Pei et al., 2022; Wang et al., 2022). MAPK cascade is a highly conserved and classical kinase.…”

“…Several phospho‐sites of AHA2, such as Thr881, Ser899, Ser944, Thr947 and other sites have been identified in Arabidopsis (Fuglsang & Palmgren, 2021; Pei et al., 2022; Wang et al., 2022). Different phosphorylation sites have different effects on the activity of PM H + ‐ATPase.…”

The EIN3/EIL‐ERF9‐HAK5 transcriptional cascade positively regulates high‐affinity K+ uptake in Gossypium hirsutum

“…The measurement of net K + uptake rate followed previously described procedures with some modifications (Wang et al ., 2022). The seedlings at the three‐leaf stage under CK or LK with equal fresh weight were taken out of the solutions and transferred to a K + ‐free solution (200 μM CaSO 4 , 5 mM MES, pH 5.7 adjusted with Tris) for 48 h. They were subsequently put into a fresh K + depletion solution (80 μM KNO 3 , 200 μM CaSO 4 , 5 mM MES, pH 5.7 adjusted with Tris).…”