Glutamate Metabolism in Plant Disease and Defense: Friend or Foe?

Abstract

Plant glutamate metabolism (GM) plays a pivotal role in amino acid metabolism and orchestrates crucial metabolic functions, with key roles in plant defense against pathogens. These functions concern three major areas: nitrogen transportation via the glutamine synthetase and glutamine-oxoglutarate aminotransferase cycle, cellular redox regulation, and tricarboxylic acid cycle-dependent energy reprogramming. During interactions with pathogens, the host GM is markedly altered, leading to either a metabolic state, termed "endurance", in which cell viability is maintained, or to an opposite metabolic state, termed "evasion", in which the process of cell death is facilitated. It seems that endurance-natured modulations result in resistance to necrotrophic pathogens and susceptibility to biotrophs, whereas evasion-related reconfigurations lead to resistance to biotrophic pathogens but stimulate the infection by necrotrophs. Pathogens, however, have evolved strategies such as toxin secretion, hemibiotrophy, and selective amino acid utilization to exploit the plant GM to their own benefit. Collectively, alterations in the host GM in response to different pathogenic scenarios appear to function in two opposing ways, either backing the ongoing defense strategy to ultimately shape an efficient resistance response or being exploited by the pathogen to promote and facilitate infection.

Metabolite profiling of sheath blight disease resistance in rice: in the case of positive ion mode analysis by CE/TOF-MS

“…It suggests that specific amino acid may associate to the susceptibility of rice plants against pathogen infection. The high concentration of some amino acid in susceptible host plants provides suitable conditions for growth and development of pathogens through nutrient supplies (Seifi et al, 2013). In addition, certain amino acid influences the pathogen development in the mechanism of pathogen infection by act as chemical exudates to attract the germination of R. solani (Keijer, 1996).…”

Metabolites and hormones are involved in the intraspecific variability of drought hardening in radiata pine

“…In P. radiata, all breeds mainly increased Pro but also accumulated other N-amino acids involved in plant glutamate metabolism (GM) such as GABA, Glu, Asn and Arg (Table 2). GM is known to play a central role in the whole plant metabolism where Glu acts as the main precursor, orchestrating crucial plant functions, including assimilation or dissimilation of ammonia, amino acid transamination and supply of C skeletons and ␣-amino groups for biosynthesis of GABA, Arg, and Pro, which play key roles in plant defense (Seifi et al, 2013). In this regard, hardening processes of P. radiata plants were also specially orchestrated firstly by Pro and secondly by GABA synthesis.…”

The metabolomics of oxidative stress

“…Interestingly, although knocking out the cytosolic isocitrate dehydrogenase, one of the contributors to 2-oxoglutarate production for the GS/GOGAT pathway, produced only a minor growth phenotype, it triggered enhanced resistance to pathogens (Mhamdi et al, 2010c). Given the central role of glutamate in carbon/nitrogen metabolism, this amino acid could play several roles in pathogenesis and other conditions involving oxidative stress (for a recent review, see Seifi et al, 2013).…”