Arabidopsis Phosphatidic Acid Phosphohydrolases Are Essential for Growth under Nitrogen-Depleted Conditions.

Yushi Yoshitake,Daisuke Sugiura,Keiko Ikeda,Masato Murakawa,Mie Shimojima,Yuka Madoka,Hiroyuki Ohta,Ryoichi Sato,Ko Suruga,Ko Noguchi

doi:10.3389/fpls.2017.01847

Abstract

The Arabidopsis homologs of mammalian lipin, PAH1 and PAH2, are cytosolic phosphatidic acid phosphohydrolases that are involved in phospholipid biosynthesis and are essential for growth under phosphate starvation. Here, pah1 pah2 double-knockout mutants were found to be hypersensitive to nitrogen (N) starvation, whereas transgenic plants overexpressing PAH1 or PAH2 in the pah1 pah2 mutant background showed a similar growth phenotype as compared with wild type (WT) under N starvation. The chlorophyll content of pah1 pah2 was significantly lower than that of WT, whereas the chlorophyll content and photosynthetic activity of the transgenic plants were significantly higher than those of WT under N-depleted conditions. Membrane glycerolipid composition of the pah1 pah2 mutants showed a significant decrease in the mole percent of chloroplast lipids to other phospholipids, whereas membrane lipid composition did not differ between transgenic plants and WT plants. Pulse-chase labeling experiments using plants grown under N-depleted conditions showed that, in pah1 pah2 plants, the labeling percent of chloroplast lipids such as phosphatidylglycerol and monogalactosyldiacylglycerol in the total glycerolipids was significantly lower than in WT. Moreover, N starvation-induced degradation of chloroplast structure was enhanced in pah1 pah2 mutants, and the membrane structure was recovered by complementation with PAH1. Thus, PAH is involved in maintaining chloroplast membrane structure and is required for growth under N-depleted conditions.

Highlights

Nitrogen (N) is an essential macronutrient for plant growth and is used to produce many fundamental biological molecules such as nucleic acids, amino acids, proteins, and metabolites (Crawford and Forde, 2002; Peng et al, 2007)
Our results showed that PAH1 and PAH2 are involved in phospholipid homeostasis in the endoplasmic reticulum (ER) and in the maintenance of the thylakoid membrane in chloroplasts and its photosynthetic activity, especially under N starvation
We previously reported that PAH is involved in Pi-starvation tolerance, because the growth of pah1 pah2 is severely impaired under Pi starvation (Nakamura et al, 2009)

Summary

Introduction

Nitrogen (N) is an essential macronutrient for plant growth and is used to produce many fundamental biological molecules such as nucleic acids, amino acids, proteins, and metabolites (Crawford and Forde, 2002; Peng et al, 2007). In Arabidopsis, the relative amount of MGDG in membrane lipids is decreased under N starvation (Gaude et al, 2007). The synthesis of fatty acid phytyl esters is enhanced in chloroplasts to avoid the accumulation of toxic intermediates, such as tetrapyrroles, free phytols, and free fatty acids, as a result of chlorophyll and galactolipid degradation during N starvation (Gaude et al, 2007). In Arabidopsis and Brassica napus, the increased expression of phospholipase Dε (PLDε), which hydrolyzes membrane phospholipids to produce the cellular signaling molecule phosphatidic acid, has the potential to improve plant growth under N-depleted conditions (Hong et al, 2009; Lu et al, 2016). Little is known about the detailed mechanism of N-starvation tolerance mediated by lipids

Methods

Results

Conclusion