Characterization of the serine acetyltransferase gene family of Vitis vinifera uncovers differences in regulation of OAS synthesis in woody plants

Abstract

In higher plants cysteine biosynthesis is catalyzed by O-acetylserine(thiol)lyase (OASTL) and represents the last step of the assimilatory sulfate reduction pathway. It is mainly regulated by provision of O-acetylserine (OAS), the nitrogen/carbon containing backbone for fixation of reduced sulfur. OAS is synthesized by Serine acetyltransferase (SERAT), which reversibly interacts with OASTL in the cysteine synthase complex (CSC). In this study we identify and characterize the SERAT gene family of the crop plant Vitis vinifera. The identified four members of the VvSERAT protein family are assigned to three distinct groups upon their sequence similarities to Arabidopsis SERATs. Expression of fluorescently labeled VvSERAT proteins uncover that the sub-cellular localization of VvSERAT1;1 and VvSERAT3;1 is the cytosol and that VvSERAT2;1 and VvSERAT2;2 localize in addition in plastids and mitochondria, respectively. The purified VvSERATs of group 1 and 2 have higher enzymatic activity than VvSERAT3;1, which display a characteristic C-terminal extension also present in AtSERAT3;1. VvSERAT1;1 and VvSERAT2;2 are evidenced to form the CSC. CSC formation activates VvSERAT2;2, by releasing CSC-associated VvSERAT2;2 from cysteine inhibition. Thus, subcellular distribution of SERAT isoforms and CSC formation in cytosol and mitochondria is conserved between Arabidopsis and grapevine. Surprisingly, VvSERAT2;1 lack the canonical C-terminal tail of plant SERATs, does not form the CSC and is almost insensitive to cysteine inhibition (IC50 = 1.9 mM cysteine). Upon sulfate depletion VvSERAT2;1 is strongly induced at the transcriptional level, while transcription of other VvSERATs is almost unaffected in sulfate deprived grapevine cell suspension cultures. Application of abiotic stresses to soil grown grapevine plants revealed isoform-specific induction of VvSERAT2;1 in leaves upon drought, whereas high light- or temperature- stress hardly trigger VvSERAT2;1 transcription.

Drought stress in maize causes differential acclimation responses of glutathione and sulfur metabolism in leaves and roots

“…The total extractable SERAT and OASTL activities were measured in order to test if the changed cysteine contents in leaves and roots were due to drought-induced changes in enzyme activities. As observed for other plant species, total OAS-TL activity was about 50–500 times higher than SERAT activities [24, 33–36], stating that the latter catalyzes the rate-limiting reaction also in maize (Fig. 4a-d).…”

Exploring traditional aus-type rice for metabolites conferring drought tolerance

“…4 ). A recent study in Vitis vinifera showed no changes of OAS concentration between WW and droughted plants, while it showed altered expression of serine acetyltransferases genes ( VvSERAT1;2 up-regulated; VvSERAT3;1 down-regulated) that convert serine to OAS (Tavares et al 2015 ). OAS is then converted to cysteine, which is the precursor of glutathione (GSH), a major antioxidant, for which accumulation under drought, cold and heat shock has been well documented (Nieto-Sotelo and Ho 1986 ; Dhindsa 1991 ; Kocsy et al 1996 ).…”

Bacteria–zinc co‐localization implicates enhanced synthesis of cysteine‐rich peptides in zinc detoxification when Brassica juncea is inoculated with Rhizobium leguminosarum

“…APS is then enzymatically converted to sulphite by APS reductase and sulphite to sulphide by the ferredoxin-dependent enzyme; sulphite reductase. The combination of sulphite with the carbon skeleton derived from serine (Ser) through O-acetylserine (OAS) synthesis under the influence of Ser acetyltransferase then yields cysteine (Saito, 2000 ; Tavares et al ., 2015 ).…”