Synergy between the anthocyanin and RDR6/SGS3/DCL4 siRNA pathways expose hidden features of Arabidopsis carbon metabolism

Nan Jiang,Blake C. Meyers,Eric Mukundi,Erich Grotewold,Aimer Gutierrez-Diaz,Marisa S. Otegui,Yun Sun Lee

doi:10.1038/s41467-020-16289-3

Abstract

Anthocyanin pigments furnish a powerful visual output of the stress and metabolic status of Arabidopsis thaliana plants. Essential for pigment accumulation is TRANSPARENT TESTA19 (TT19), a glutathione S-transferase proposed to bind and stabilize anthocyanins, participating in their vacuolar sequestration, a function conserved across the flowering plants. Here, we report the identification of genetic suppressors that result in anthocyanin accumulation in the absence of TT19. We show that mutations in RDR6, SGS3, or DCL4 suppress the anthocyanin defect of tt19 by pushing carbon towards flavonoid biosynthesis. This effect is not unique to tt19 and extends to at least one other anthocyanin pathway gene mutant. This synergy between mutations in components of the RDR6-SGS3-DCL4 siRNA system and the flavonoid pathway reveals genetic/epigenetic mechanisms regulating metabolic fluxes.

Highlights

Anthocyanin pigments furnish a powerful visual output of the stress and metabolic status of Arabidopsis thaliana plants
The alignment of SUPPRESSOR OF GENE SILENCING 3 (SGS3) transcript reads from S5 suggested an alternative splicing site 15 nt downstream of nucleotide 2,283 that resulted in the deletion of five amino acids (Fig. 1b)
No other pathway intermediate was found to accumulate in tt[] to explain the significantly lower levels of anthocyanins in this mutant. These results demonstrate that the combination of mutations in TT19 and either RDR6, SGS3, or DICER-LIKE 4 (DCL4) results in metabolic changes that are significantly different from those found in the single mutants, suggesting a synergistic cross-talk between cellular processes controlled by the RDR6-SGS3-DCL4 system and those modulated by TT19

Summary

Introduction

Anthocyanin pigments furnish a powerful visual output of the stress and metabolic status of Arabidopsis thaliana plants. We show that mutations in RDR6, SGS3, or DCL4 suppress the anthocyanin defect of tt[19] by pushing carbon towards flavonoid biosynthesis This effect is not unique to tt[19] and extends to at least one other anthocyanin pathway gene mutant. The extensive knowledge on anthocyanin biosynthesis enzymes from many plants contrasts with how little is known about the mechanisms by which these pigments are transported from their site of synthesis to the vacuole[5,6] Key players in this process are a group of conserved glutathione S-transferase (GST) proteins and ABC transporters that interact with anthocyanins[7,8,9] and are believed to facilitate their transport across the tonoplast[10,11]. TT19 is controlled by the R2R3-MYB transcription factor PRODUCTION OF ANTHOCYANIN1 (PAP1/MYB75)[14,15], and to a lesser extent, PAP2/MYB90, MYB113 and MYB11416,17

Methods

Results

Conclusion