Identification and characterisation of novel components in glucosinolate biosynthesis and regulation
Final Report Abstract
Within the project "Identification and characterisation of novel components in glucosinolate biosynthesis and Regulation" we can demonstrate, that to control the GSL biosynthetic pathway plants does not solely require the MYB transcription factors, but also need the bHLH proteins. We propose a model in which MYBs and bHLHs are recruited to the promoters of "GSL" synthesis genes to activate their transcription. The MYB proteins bind to MYB-boxes, whereas bHLH proteins bind to G-boxes. We believe that the function of bHLHs is to tether the mediator complex and chromatin-modifying factors to DNA, which unwind chromatin and make it accessible to MYBs and the RNA polymerase II transcription apparatus, which activates the transcription of GSL biosynthesis genes. Furthermore, we analysed the distinct regulatory role of different MYBs in the regulation of indolic GSLs and demonstrated that MYB34, MYB51 and MYB122 respond differently to ABA, SA, JA and ET: (i) MYB51 is a central regulator of IG synthesis upon SA and ET signalling, (ii) MYB34 is the key regulator upon ABA and JA signalling and (iii) MYB122 plays a minor role in JA/ET-induced glucosinolate biosynthesis. In addition, we addressed the role of the responsiveness of MYBs in controlling the production of indolic and aliphatic glucosinolates to sulphur deficiency conditions. Here, we showed that the decrease in the concentrations of GSLs during S depletion does not coincide with the intuitively expected decrease in the transcription of all "R2R3-MYBs". The expression of "MYB51", "MYB122" and "MYB28" is counterintuitively increased and the expression of "MYB29" and "MYB76" is decreased under prolonged S starvation. Finally, we can show that SLIM1 which is known as glucosinolate biosynthesis regulator directly represses the promoters of "MYB" genes. However, in vivo, the mRNA of "MYB28", "MYB51" and "MYB34" correlated with the decreased GSL levels in sulphur-deficient conditions. We propose a model where the negative effect of SLIM1 on GSL regulatory genes can be overridden by a "low GSL Signal", which induces the transcription of "MYB51" and "MYB28" in a feedback regulatory loop. Along with the identification of new components in glucosinolate regulation, we also identified new structural genes of this pathway. We can show that an antiporter of 3'-phosphoadenosine-5'-phosphosulphate (PAPS) and of 3'-phosphoadenosine 5'-phosphate (PAP), is required for the biosynthesis of GSLs and also other sulphated metabolites in plants. The PAPS transporter, PAPST1, is present in the chloroplast envelope membrane and is involved in the provision of PAPS for extra-plastidic sulphation reactions, but can also transport PAP in an antiport manner. In addition to PAPST1, we have recently identified PAPST2 as a second chloroplastidic antiporter, which can transport PAPS and PAP in vitro. The double "papst1/papst2" mutant is lethal and the basis of the lethality of PAPS deficiency in plant cells is being recently uncovered.
Publications
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(2012) Glucosinolates are produced in trichomes of A.thaliana. Frontiers in Plant Science. 3: 242
Frerigmann H, Böttcher C, Baatout D, Scheel D, Flügge, UI and Gigolashvili T
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(2012) The Arabidopsis thylakoid ADP/ATP carrier TAAC has a primary role in supplying plastidic phosphoadenosine 5´-phosphosulfate (PAPS) to the cytosol. The Plant Cell 24: 4187-4204
Gigolashvili T, Geier M, Ashykhmina N, Frerigmann F, Wulfert S, Krueger S, Mugford SG, Kopriva S, Haferkamp I and Flügge UI
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(2014) bHLH05 is an interaction partner of MYB51 and a novel regulator of glucosinolate biosynthesis in Arabidopsis thaliana. Plant Phyiology. 166: 349-369
Frerigmann H, Berger B and Gigolashvili T
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(2014) The three MYB transcription factors MYB34, MYB51 and MYB122 exert distinct regulation on indolic glucosinolate biosynthesis in Arabidopsis thaliana. Molecular Plant. 7 (5): 814-828
Frerigmann H and Gigolashvili T
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(2014) Transporters in plant sulfur metabolism. Frontiers in Plant Science Sep 9;5: 442
Gigolashvili T and Kopriva S
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(2014) Update on the role of R2R3-MYBs in the regulation of glucosinolates upon sulfur deficiency. Frontiers in Plant Science. 5(626): 1-10
Frerigmann H and Gigolashvili T
