Glutamate dehydrogenase isogenes CsGDHs cooperate with glutamine synthetase isogenes CsGSs to assimilate ammonium in tea plant (Camellia sinensis L.).

Abstract Glutamate dehydrogenase (GDH) is a central enzyme in nitrogen metabolism, assimilating ammonia into glutamine or deaminating glutamate into α-oxoglutarate. Tea (Camellia sinensis L.) plants assimilate ammonium efficiently, but the role of CsGDH in ammonium assimilation remains unclear. We confirmed that tea has three GDH isogenes: CsGDH1-3. Bioinformatic analysis showed that CsGDH1 encodes the β-GDH subunit, CsGDH2/3 encode the α-GDH subunit, and their proteins all feature an NADH-specific motif. CsGDH1 is mainly expressed in mature leaves and roots, CsGDH3 is mainly expressed in new shoots and roots, and CsGDH2 has the highest expression level in flowers compared to the other five tissues. Expression patterns of CsGDHs and glutamine synthetase isogenes (CsGSs) under different ammonium concentrations suggested that CsGDHs cooperate with CsGSs to assimilate ammonium, especially under high ammonium conditions. Inhibition of GS and its isogenes resulted in significant induction of CsGDH3 in roots and CsGDH2 in leaves, indicating their potential roles in ammonium assimilation. Moreover, CsGDHs transcripts were highly abundant in chlorotic tea leaves, in constrast to those of CsGSs, suggesting that CsGDHs play a vital role in ammonium assimilation in chlorotic tea mutant. Altogether, our circumstantial evidence that CsGDHs cooperate with CsGSs in ammonium assimilation provides a basis for unveiling their functions in tea plants.