Arabidopsis inositol phosphate kinases IPK1 and ITPK1 constitute a metabolic pathway in maintaining phosphate homeostasis. (15th June 2018)

• Record Type: Journal Article
• Authors: Kuo, Hui‐Fen; Hsu, Yu‐Ying; Lin, Wei‐Chi; Chen, Kai‐Yu; Munnik, Teun; Brearley, Charles A.; Chiou, Tzyy‐Jen
• Is Part Of: Plant journal. Volume 95:Number 4(2018)
• Page Start: 613
• Page End: 630
• Publication Date: 2018-06-15
• Subjects: inositol phosphate -- inositol pentakisphosphate 2‐kinase (IPK1) -- inositol 1, 3, 4‐trisphosphate 5/6‐kinase 1 (ITPK1) -- phosphate homeostasis -- d/l‐inositol 3, 4, 5, 6‐tetrakisphosphate -- phosphate starvation response -- diphosphoinositol pentakisphosphate -- phytate biosynthesis -- Arabidopsis thaliana; Plant molecular biology -- Periodicals; Plant cells and tissues -- Periodicals; Botany -- Periodicals; 580
• DOI: 10.1111/tpj.13974
• Languages: English
• ISSNs: 0960-7412

Abstract

Summary: Emerging studies have suggested that there is a close link between inositol phosphate (InsP) metabolism and cellular phosphate (Pi ) homeostasis in eukaryotes; however, whether a common InsP species is deployed as an evolutionarily conserved metabolic messenger to mediate Pi signaling remains unknown. Here, using genetics and InsP profiling combined with Pi ‐starvation response (PSR) analysis in Arabidopsis thaliana, we showed that the kinase activity of inositol pentakisphosphate 2‐kinase (IPK1), an enzyme required for phytate (inositol hexakisphosphate; InsP6 ) synthesis, is indispensable for maintaining Pi homeostasis under Pi ‐replete conditions, and inositol 1, 3, 4‐trisphosphate 5/6‐kinase 1 (ITPK1) plays an equivalent role. Although both ipk1‐1 and itpk1 mutants exhibited decreased levels of InsP6 and diphosphoinositol pentakisphosphate (PP‐InsP5 ; InsP7 ), disruption of another ITPK family enzyme, ITPK4, which correspondingly caused depletion of InsP6 and InsP7, did not display similar Pi ‐related phenotypes, which precludes these InsP species from being effectors. Notably, the level ofd /l ‐Ins(3, 4, 5, 6)P4 was concurrently elevated in both ipk1‐1 and itpk1 mutants, which showed a specific correlation with the misregulated Pi phenotypes. However, the level ofd /l ‐Ins(3, 4, 5, 6)P4 is not responsive to Pi starvation that instead manifests a shoot‐specific increase in the InsP7 level. This study demonstrates a more nuanced picture of the intersection of InsP metabolism and Pi homeostasis and PSRs than has previously been elaborated, and additionally establishes intermediate steps to phytate biosynthesis in plant vegetative tissues. Significance Statement: Regulation of phosphate homeostasis and adaptive responses to phosphate limitation are critical for plant growth and crop yield. Studies have implicated inositol phosphates as regulators of phosphate homeostasis in eukaryotes; however, the relationship between inositol phosphate metabolism and phosphate signaling in plants remains elusive. This study dissected the step in which inositol phosphate metabolism intersects with regulation of phosphate homeostasis and phosphate starvation responses.