Identification of C-S lyases functioning in glucosinolate biosynthesis in Arabidopsis thaliana

Abstract Description:

Glucosinolates are defense compounds found in Brassicales including Arabidopsis thaliana. Arabidopsis accumulates over 30 types of glucosinolates and the composition and content of glucosinolates vary organ to organ. Glucosinolate biosynthesis requires carbon-sulfur lyase (C-S lyase) activity to convert S-alkylthiohydroximates to thiohydroximate intermediates of glucosinolates. In Arabidopsis, SUPERROOT1 (SUR1) is the only characterized C-S lyase functioning in glucosinolate biosynthesis. Due to the excessive increase of indole acetic acid (IAA) redirected from the upstream accumulation of indole-3-acetalaldoxime (IAOx) in sur1, sur1 exhibits auxin accumulation morphological changes including severe dwarfism, which indirectly indicates its predominant role as C-S lyase in glucosinolate biosynthesis. However, as sur1 does not develop beyond seedling stage, it is infeasible to determine any functions of SUR1 in most organs including seeds, which are rich in glucosinolates. To determine SUR1 function in glucosinolate biosynthesis in Arabidopsis seeds, we generated sur1 mutants in the absence of IAOx. CYP79B2 and CYP79B3 function redundantly to produce IAOx in Arabidopsis and cyp79b2 and cyp79b3 (b2b3) double mutants are absent in IAOx but grow like wild type. By knocking out SUR1 in b2b3, we generated b2b3sur1 triple mutants. b2b3sur1 mutants successfully rescued the severe dwarfism observed in sur1 and produce seeds. Our metabolite analysis uncovered that b2b3sur1 did not completely block all glucosinolates in seeds and SUR1 was dispensable for some glucosinolates, indicating existence of other C-S lyases playing roles in glucosinolate biosynthesis. Transcriptomic and metabolomic analysis helped identify possible candidates for alternative C-S lyases in glucosinolate biosynthesis in Arabidopsis thaliana.

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