Alanine aminotransferase variants conferring diverse NUE phenotypes in Arabidopsis thaliana.

Chandra H Mcallister,Allen G Good,Panagiotis Kalaitzis

doi:10.1371/journal.pone.0121830

Abstract

Alanine aminotransferase (AlaAT, E.C. 2.6.1.2), is a pyridoxal-5’-phosphate-dependent (PLP) enzyme that catalyzes the reversible transfer of an amino group from alanine to 2-oxoglutarate to produce glutamate and pyruvate, or vice versa. It has been well documented in both greenhouse and field studies that tissue-specific over-expression of AlaAT from barley (Hordeum vulgare, HvAlaAT) results in a significant increase in plant NUE in both canola and rice. While the physical phenotypes associated with over-expression of HvAlaAT have been well characterized, the role this enzyme plays in vivo to create a more N efficient plant remains unknown. Furthermore, the importance of HvAlaAT, in contrast to other AlaAT enzyme homologues in creating this phenotype has not yet been explored. To address the role of AlaAT in NUE, AlaAT variants from diverse sources and different subcellular locations, were expressed in the wild-type Arabidopsis thaliana Col-0 background and alaat1;2 (alaat1-1;alaat2-1) knockout background in various N environments. The analysis and comparison of both the physical and physiological properties of AlaAT over-expressing transgenic plants demonstrated significant differences between plants expressing the different AlaAT enzymes under different external conditions. This analysis indicates that the over-expression of AlaAT variants other than HvAlaAT in crop plants could further increase the NUE phenotype(s) previously observed.

Highlights

As sessile organisms, the growth and development of plants is highly reliant on their ability to rapidly sense and adjust to changes in their environment
We demonstrate that plant responses to N as well as C can be altered significantly by over-expressing AlaAT in A. thaliana, and that these nitrogen use efficiency (NUE) responses can be significantly influenced by over-expression of a particular AlaAT enzyme variant
All three transgenic lines carrying Pyrococcus furiosus AlaAT (PfAlaAT) showed significantly increased uptake of both alanine and leucine; this was the only AlaAT to have all independent insertion lines demonstrate significantly increased uptake of both amino acids (Fig. 8). These results indicate that the amino acid/N concentration in PfAlaAT-expressing mesophyll cells is significantly altered relative to Col-0 and the other transgenic lines analyzed, presumably due to alterations in N assimilation and mobilization/remobilization within the plant

Summary

Introduction

The growth and development of plants is highly reliant on their ability to rapidly sense and adjust to changes in their environment. Response patterns to internal and external signals can have both immediate and long lasting effects, affecting current and overall growth and development of the plant [1,2,3,4,5,6]. Nitrogen (N) availability and form (organic or inorganic) is known to strongly impact plant physiology, including N metabolism, carbon (C) metabolism and plant signalling [7,8,9,10]. Plants that more effectively uptake, allocate or remobilize available N are said to have increased nitrogen use efficiency (NUE) [11,12]. While many different definitions of NUE have been developed over time, depending on the physiological

Methods

Results

Conclusion