γ-aminobutyric acid (GABA) is a nonproteinogenic amino acid which is mainly synthesized from alpha-decarboxylation of glutamate (Glu) catalysed by glutamate decarboxylase (GAD). GABA accumulates under a variety of stress conditions of which salinity and flooding are among the most intractable abiotic stresses that plant face. GABA accumulation occurs to the greatest extent during hypoxia and anoxia, however, its exact role is still to be elucidated.
Here we study the role of GABA during submergence stress in Arabidopsis thaliana. The materials used include Arabidopsis wildtype and mutants (Col-0): GABA-depleted lines (gad1, gad2 and gad1/2/4/5), GABA-accumulating lines by either GABA-T deficiency (pop2) or GAD2-overexpression (B33 and B97).
In the salt experiment, pop2 total root length is significantly larger than WT after 9 days on ½ MS, mainly because their lateral roots developed faster, and this is brought down by 50 mM NaCl treatment to WT level. Interestingly, gad1/2/4/5 and pop2 have a greater primary root Relative Elongation Rate (RER) than WT on 1/2MS but not under salt, while these were not seen in B33 or B97.
In the hypoxia experiment, preliminary results of Relative Water Content (RWC), photosynthesis system Ⅱ (Fv/Fm) and phenotyping showed that pop2 and gad2 was the most and least sensitive respectively during a 6-day submergence. Other mutants were not affected compared to wildtype and were able to recover after 3-day de-submerge, while pop2 couldn’t.
RNAseq and metabolites data analysis currently being performed will allow us to have a clearer and deeper understanding of whether GABA accumulates only as a result of metabolic perturbation under stress, or if GABA has a critical function for flooding tolerance.