Fiat lux!

Abstract

Gamma-aminobutyric acid (GABA), a four-carbon non-protein amino acid, has drawn much attention since its first identification over 60 y ago in potato tuber, 1 rat brain 2 and yeast extract. 3Subsequent investigations of GABA functions followed two main directions: signaling and metabolism. Signaling effects of GABA have been intensively tackled in mammalian models. It has been clearly established that GABA acts as a neurotransmitter 4 and impacts the central nervous system development. 5,6 In plants, early studies in the 70-80s reported rapid GABA accumulation in response to many environmental cues.7-10 Based on these observations, it has been hypothesized that GABA could participate in stress responses and tolerance. Nevertheless, for decades, GABA functions in plants remained elusive. Major progress came along with the genomic era and availability of the powerful embedded tools. Genetic analyses in Arabidopsis demonstrated that GABA acts as a signal molecule for pollen tube guidance and elongation.11,12 Alteration of tricarboxylic acid (TCA) cycle enzyme activities shed light on GABA metabolic function and stressed the tight connection between GABA and respiration. [13][14][15] The functional implication of GABA metabolism in Arabidopsis salt stress tolerance has recently been reported. 16,17 The GABA transaminase gaba-t/pop2-1 mutant root growth was shown hypersensitive to the ionic component of salt stress, 16 confirming the long-standing hypothesis of GABA involvement in plant stress response. Metabolic data revealed that GABA bridges amino and organic acids metabolisms in roots underThe non-protein amino acid γ-aminobutyric acid (GABA) accumulates in plants in response to a wide variety of environmental cues. Recent data point toward an involvement of GABA in tricarboxylic acid (TCA) cycle activity and respiration, especially in stressed roots. To gain further insights into potential GABA functions in plants, phylogenetic and bioinformatic approaches were undertaken. Phylogenetic reconstruction of the GABA transaminase (GABA-T) protein family revealed the monophyletic nature of plant GABA-Ts. However, this analysis also pointed to the common origin of several plant aminotransferases families, which were found more similar to plant GABA-Ts than yeast and human GABA-Ts. A computational analysis of AtGABA-T co-expressed genes was performed in roots and in stress conditions. This second approach uncovered a strong connection between GABA metabolism and glyoxylate cycle during stress. Both in silico analyses open new perspectives and hypotheses for GABA metabolic functions in plants. Keywords: GABA-T, evolution, glyoxylate cycle, lipids, respiration, root, stress saline conditions. 16,17 Moreover, a genome-wide transcriptional analysis indicated that central carbon metabolism is altered upon the loss of GABA metabolic function during salt stress. Indeed, genes involved in remobilization of carbon reserves (i.e., sucrose and starch) were found higher expressed in the gaba-t/pop2-1 mutant. Fiat lux!17 However, de...

Closing the loop on the GABA shunt in plants: are GABA metabolism and signaling entwined?

“…Changes in the cellular distribution and quantity of GABA were shown also to affect levels of several AAs in different plant species ( Baum et al, 1996 ; Michaeli et al, 2011 ; Deleu et al, 2013 ; Shimajiri et al, 2013a ; Batushansky et al, 2014 ; Snowden et al, 2015 ) and even in seeds ( Fait et al, 2011 ). As a molecule synthesized mainly from glutamate, yet intimately associated with the TCAC, GABA is continuously suggested to be an important component in the balance between C and nitrogen (C:N) pools of plant cells ( Fait et al, 2008 ; Renault, 2013 ; Batushansky et al, 2014 ).…”

An evolutionary view of vanillylamine synthase pAMT, a key enzyme of capsaicinoid biosynthesis pathway in chili pepper

“…In order to clarify the phylogenetic relationship between pAMT and other plant GABA‐Ts, a phylogenetic tree was constructed. In total, 42 aminotransferases including various plant GABA‐Ts were used, in accordance with a previous report (Renault, 2013). In addition, a total of 13 Solanaceae GABA‐Ts that showed >75% homology to pAMT (CA03g08530 in CM344 genome) were collected in the Sol Genomics (https://solgenomics.net/) and NCBI (http://blast.ncbi.nlm.nih.gov/Blast.cgi) databases.…”

“…pAMT is indicated with a red star. Human and yeast GABA-T protein and Arabidopsis proteins related to AtGABA-T were included as outgroups, in accordance with Renault et al (2013). The numbers beside the branches represent bootstrap support values from 1000 replications.…”

Amino Acids of the Glutamate Family: Functions beyond Primary Metabolism

“…Changes in the cellular distribution and quantity of GABA were shown also to affect levels of several AAs in different plant species Deleu et al, 2013;Shimajiri et al, 2013a; and even in seeds . As a molecule synthesized mainly from glutamate, yet intimately associated with the TCAC, GABA is continuously suggested to be an important component in the balance between C and nitrogen (C:N) pools of plant cells Renault, 2013;.…”