ABI4 Activates DGAT1 Expression in Arabidopsis Seedlings during Nitrogen Deficiency

Yang Yang,Chengcai An,Lianfen Song,Xiangchun Yu

doi:10.1104/pp.111.175950

Abstract

Triacylglycerol (TAG) is the major seed storage lipid and is important for biofuel and other renewable chemical uses. Acyl-coenzyme A:diacylglycerol acyltransferase1 (DGAT1) is the rate-limiting enzyme in the TAG biosynthesis pathway, but the mechanism of its regulation is unknown. Here, we show that TAG accumulation in Arabidopsis (Arabidopsis thaliana) seedlings increased significantly during nitrogen deprivation (0.1 mm nitrogen) with concomitant induction of genes involved in TAG biosynthesis and accumulation, such as DGAT1 and OLEOSIN1. Nitrogen-deficient seedlings were used to determine the key factors contributing to ectopic TAG accumulation in vegetative tissues. Under low-nitrogen conditions, the phytohormone abscisic acid plays a crucial role in promoting TAG accumulation in Arabidopsis seedlings. Yeast one-hybrid and electrophoretic mobility shift assays demonstrated that ABSCISIC ACID INSENSITIVE4 (ABI4), an important transcriptional factor in the abscisic acid signaling pathway, bound directly to the CE1-like elements (CACCG) present in DGAT1 promoters. Genetic studies also revealed that TAG accumulation and DGAT1 expression were reduced in the abi4 mutant. Taken together, our results indicate that abscisic acid signaling is part of the regulatory machinery governing TAG ectopic accumulation and that ABI4 is essential for the activation of DGAT1 in Arabidopsis seedlings during nitrogen deficiency.

Highlights

Triacylglycerol (TAG) is the major seed storage lipid and is important for biofuel and other renewable chemical uses
In Arabidopsis seedlings, Glc and abscisic acid (ABA) actively regulate the transcription of ACYL-COENZYME A:DIACYLGLYCEROL ACYLTRANSFERASE1 (DGAT1), which is crucial for TAG biosynthesis (Lu et al, 2003), the exact molecular mechanism has not been determined
Neither the T-DNA insertion nor the overexpression of PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE1 (PDAT1) in Arabidopsis alters the seed oil content (Stahl et al, 2004; Mhaske et al, 2005), RNA interference silencing of PDAT1 in the Arabidopsis dgat1 background results in a 63% decrease in oil content compared with the dgat1 control (Zhang et al, 2009), which indicates that PDAT1 is the gene responsible for most of the TAG synthesis in the dgat1 mutant

Summary

Introduction

Triacylglycerol (TAG) is the major seed storage lipid and is important for biofuel and other renewable chemical uses. Under low-nitrogen conditions, the phytohormone abscisic acid plays a crucial role in promoting TAG accumulation in Arabidopsis seedlings. Our results indicate that abscisic acid signaling is part of the regulatory machinery governing TAG ectopic accumulation and that ABI4 is essential for the activation of DGAT1 in Arabidopsis seedlings during nitrogen deficiency. In Arabidopsis seedlings, Glc and ABA actively regulate the transcription of ACYL-COENZYME A:DIACYLGLYCEROL ACYLTRANSFERASE1 (DGAT1), which is crucial for TAG biosynthesis (Lu et al, 2003), the exact molecular mechanism has not been determined. Despite extensive reports mentioning the accumulation of storage oil in leaves, none of these studies have addressed the mechanisms or the factors that regulate the expression of key genes in TAG metabolism. Our study demonstrates a regulation mechanism of DGAT1 in Arabidopsis seedlings

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Discussion

Conclusion