Phosphatidylinositol kinases as regulators of GA‐stimulated α‐amylase secretion in barley (Hordeum vulgare)

Abstract

Phosphorylated derivatives of phosphatidylinositol, in association with phosphatidylinositol 3-kinase (PI3 kinase, EC 2.7.1.137) and phosphatidylinositol 4-kinase (PI4 kinase, EC 2.7.1.67), play a key role in regulation of fundamental cell processes. We present evidence for a relationship between alpha-amylase (EC 3.2.1.1) secretion regulated by GA and levels of phosphatidylinositol 3-phosphate and phosphatidylinositol 4-phosphate (PtdIns(4)P) in barley (Hordeum vulgare). Microsomal membranes were incubated in the presence of [gamma-(32)P]ATP, and radiolabeled membrane lipids were extracted and separated by TLC using a boric acid system. Treatment of aleurone layers with GA for short or long periods of time increased PI4 kinase activity. To evaluate the effect of PtdIns(4)P levels on GA signaling, we used phenylarsine oxide (PAO), an inhibitor of PI4 kinase activity. PAO reversibly reduced the alpha-amylase secretion and protoplast cell vacuolation in a dose-dependent manner. Wortmannin showed a similar inhibitory effect on alpha-amylase secretion and PI4 kinase activity. GA evoked only a long-term increase in PI3 kinase activity, which was also affected by PAO. The effect of PAO was suppressed by the reducing agent 2,3-dimercapto-1-propanol (BAL), leading to restoration of secretion, vacuolation and PI4 kinase activity. In contrast, the effect of PAO on PI3 kinase activity was not abolished by BAL, suggesting that PI3 kinase is not involved in the secretion process. Likewise, the compound LY294002 inhibited PI3 kinase but had no effect on the secretion process. These findings indicate that PI4 kinase acts as a positive regulator of early GA signaling in aleurone.

Effect of Deteriorated Seed Soaking with Different Concentrations of Gibberellin (GA3) on Germination and Seedling Growth of Two Oat (Avena sativa L.) Cultivars

“…In the early germination phase, the embryo produces an effective factor (gibberellin), which is transferred to the aleurone cells to activate the genes controlling the synthesis of enzymes, which lead to producing energy and necessary proteins to format new cellular components. This is in line with what mentioned by Lovegrove and Hooley (2000), Richards et al (2001), Subedi and Bhattarai (2003), Chen et al (2008) and Villasuso et al (2008).…”

Integrated mRNA and miRNA transcriptome analysis reveals regulatory network of yam tuber expansion

“…MAPK signal related genes were up-regulated during expansion stage. MAPK signal pathway increased PI3K pathway, which in turn led to elevate GA levels, and generate calcium signals [68][69][70]. Moreover, MAPK signal pathway is known to play a central role in cell proliferation, differentiation and hormone signaling [50,51].…”

Co-opted Cellular Sac1 Lipid Phosphatase and PI(4)P Phosphoinositide Are Key Host Factors during the Biogenesis of the Tombusvirus Replication Compartment

“…To confirm the role of PI(4)P in plants, we used phenylarsine oxide (PAO), a specific inhibitor of PI(4)P kinases (72,73) in N. benthamiana protoplasts replicating TBSV gRNA. PAO treatment resulted in undetectable accumulation of TBSV RNAs in plant cells (Fig.…”

“…Isolation of protoplasts from N. benthamiana leaves were carried out as described previously (26). The isolated protoplasts were transfected with TBSV genomic RNA isolated from infected plants using polyethylene glycol (PEG) (104) and treated with 50 M PAO, a PI4K inhibitor (72,73). Sixteen hours after transfection, the protoplasts were harvested by centrifugation and analyzed for TBSV levels by Northern blotting analysis.…”