RESUMEN
Potassium (K+) is a vital cation and is involved in multiple physiological functions in plants. K+ uptake from outer medium by roots is a tightly regulated process and is mainly carried out by two high affinity K+ transport proteins AKT1 and HAK5. It has been shown that calcium (Ca2+) signaling plays important roles in the regulation of K+ transport in plants. Ca2+-dependent protein kinases (CPKs) are involved in regulation of multiple K+ channels in different tissues. However, it remains to be studied whether CPKs are involved in the regulation of AKT1 and, thereby, K+ transport. Here, we have shown that constitutively active version of CPK3 (CPK3CA) is involved in K+ transport in Arabidopsis via regulating AKT1 under low K+ conditions. The constitutively active version of CPK3 (CPK3CA), as well as CPK21 (CPK21CA), inhibited K+ currents of AKT1 in Xenopus oocytes. CPK3CA inhibited only channel conductance but had no effect on channel open probability. Further, CPK3 in vivo interacted with AKT1. Under low K+ conditions, cpk3 knock-out mutants had no distinct phenotype, while the seedlings of 35S-CPK3CA overexpressing lines died even at normal K+ concentration. Further, the transgenic lines expressing CPK3CA under AKT1 promoter (ProAKT1-CPK3CA) exhibited the same phenotype as akt1 mutant with a defective root growth and leaf chlorosis. Moreover, ProAKT1-CPK3CA transgenic lines had lower root and shoot K+ contents than Col. Overall, the data reported here demonstrate that the expression of constitutively active of CPK3 impairs potassium uptake and transports in Arabidopsis under low K+ stress by inhibiting the activity of AKT1.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Raíces de Plantas/metabolismo , Potasio/metabolismo , Canales de PotasioRESUMEN
Two full-length cDNAs, PutPMP3-1 and PutPMP3-2, encoding PMP3 family proteins were isolated from Puccinellia tenuiflora, a monocotyledonous halophyte. Expression of both genes was induced by low temperature, salt stress, dehydration, ABA, and NaHCO(3). Transcripts of PutPMP3-2 were more strongly induced by these stresses relative to those of PutPMP3-1, particularly under low temperature and dehydration conditions. Expression of PutPMP3-1 and PutPMP3-2 in yeast mutants lacking the PMP3 gene can functionally complement the membrane hyperpolarization and salt sensitivity phenotypes resulting from PMP3 deletion. To compare the functions of PutPMP3-1 and PutPMP3-2, the orthologous genes in rice (OsLti6a and OsLti6b) were isolated. Both OsLti6a and OsLti6b could functionally complement the loss of PMP3 in yeast. PutPMP3-2 and OsLti6a were more effective in reversing membrane hyperpolarization than PutPMP3-1 and OsLti6b. However, the four yeast transformants each showed similar levels of salt tolerance. These results imply that these PMP3 family members don't function identically under different stress tolerance conditions.