NIN-like protein 8 is a master regulator of nitrate-promoted seed germination in Arabidopsis.

Dawei Yan,Eiji Nambara,Asher Pasha,Vanathy Easwaran,David Guttman,Ryoichi Yano,Yunchen Gong,Matthew Ierullo,Steven J Rothstein,Anne Krapp,Mitsuhiro Kimura,Vivian Chau,Masanori Okamoto,Nicolas Provart,Akira Endo,Yong-Mei Bi

doi:10.1038/ncomms13179

Abstract

Seeds respond to multiple different environmental stimuli that regulate germination. Nitrate stimulates germination in many plants but how it does so remains unclear. Here we show that the Arabidopsis NIN-like protein 8 (NLP8) is essential for nitrate-promoted seed germination. Seed germination in nlp8 loss-of-function mutants does not respond to nitrate. NLP8 functions even in a nitrate reductase-deficient mutant background, and the requirement for NLP8 is conserved among Arabidopsis accessions. NLP8 reduces abscisic acid levels in a nitrate-dependent manner and directly binds to the promoter of CYP707A2, encoding an abscisic acid catabolic enzyme. Genetic analysis shows that NLP8-mediated promotion of seed germination by nitrate requires CYP707A2. Finally, we show that NLP8 localizes to nuclei and unlike NLP7, does not appear to be activated by nitrate-dependent nuclear retention of NLP7, suggesting that seeds have a unique mechanism for nitrate signalling.

Highlights

Seeds respond to multiple different environmental stimuli that regulate germination
On the basis of the microarray data from seeds imbibed for o6 h, we selected candidate regulators for nitrate signalling in seeds and analysed whether or not corresponding T-DNA insertion mutants displayed nitrate-induced seed germination
Time course expression analysis showed that NIN-like protein 8 (NLP8)-dependent nitrate induction is transient and is not seen in 12-h imbibed seeds (Fig. 3b,c), suggesting that a repressive mechanism comes into play to downregulate expression of NLP8-reglated genes in the latter stages of seed imbibition

Summary

Introduction

Seeds respond to multiple different environmental stimuli that regulate germination. NLP8 reduces abscisic acid levels in a nitrate-dependent manner and directly binds to the promoter of CYP707A2, encoding an abscisic acid catabolic enzyme. Genetic analysis shows that NLP8-mediated promotion of seed germination by nitrate requires CYP707A2. A transcriptome analysis revealed that different germination stimuli trigger a similar transcriptome pattern[1] This suggests that these environmental factors regulate a common downstream event, such as plant hormone action. ABA and GA metabolism and signalling respond to changing environmental factors and induce downstream events suitable for the given environment. CYP707A1 plays a role in the degradation of ABA that occurs during the mid-maturation stage of seed development. Other nitrogen-containing compounds such as nitrite, nitric oxide (NO) and cyanides promote Arabidopsis seed germination[13]. Identification of the nitrate signalling components in seeds, is crucial for evaluating the mechanism of nitrate action on germination in relation to other germination stimulating signalling pathways including NO

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Results

Conclusion