A Trafficking Pathway for Anthocyanins Overlaps with the Endoplasmic Reticulum-to-Vacuole Protein-Sorting Route in Arabidopsis and Contributes to the Formation of Vacuolar Inclusions

Abstract

Plants produce a very large number of specialized compounds that must be transported from their site of synthesis to the sites of storage or disposal. Anthocyanin accumulation has provided a powerful system to elucidate the molecular and cellular mechanisms associated with the intracellular trafficking of phytochemicals. Benefiting from the unique fluorescent properties of anthocyanins, we show here that in Arabidopsis (Arabidopsis thaliana), one route for anthocyanin transport to the vacuole involves vesicle-like structures shared with components of the secretory pathway. By colocalizing the red fluorescence of the anthocyanins with green fluorescent protein markers of the endomembrane system in Arabidopsis seedlings, we show that anthocyanins are also sequestered to the endoplasmic reticulum and to endoplasmic reticulum-derived vesicle-like structures targeted directly to the protein storage vacuole in a Golgi-independent manner. Moreover, our results indicate that vacuolar accumulation of anthocyanins does not depend solely on glutathione S-transferase activity or ATP-dependent transport mechanisms. Indeed, we observed a dramatic increase of anthocyanin-filled subvacuolar structures, without a significant effect on total anthocyanin levels, when we inhibited glutathione S-transferase activity, or the ATP-dependent transporters with vanadate, a general ATPase inhibitor. Taken together, these results provide evidence for an alternative novel mechanism of vesicular transport and vacuolar sequestration of anthocyanins in Arabidopsis.

Evaluating the involvement and interaction of abscisic acid and miRNA156 in the induction of anthocyanin biosynthesis in drought-stressed plants

“…The transport of anthocyanins by PVCs has been described in Vitis vinifera (Conn et al 2003), Arabidopsis thaliana (Poustka et al 2007), and Sorghum bicolor (Snyder and Nicholson 1990). Anthocyanins have been shown to accumulate in the RER lumen (Poustka et al 2007); therefore, these PVC structures could be originated within the RER lumen. PVCs can enter the vacuole by either endocytosis (Gómez et al 2011) or directly into the vacuole by microautophagy as the vacuolar membrane engulfs anthocyanins (Chanoca et al 2015).…”

COP1-Mediated Degradation of BBX22/LZF1 Optimizes Seedling Development in Arabidopsis

“…Our results suggest that the selective degradation of BBX22 might fine-tune the expression of ELIP2 for optimal chlorophyll accumulation. BBX22 also up-regulates genes involved in flavonoid and anthocyanin biosynthesis pathways, including CHS, CHI, F3H, and 4CL3 (Li et al, 1993;Shirley et al, 1995;Ehlting et al, 1999;Raes et al, 2003;Solfanelli et al, 2006;Poustka et al, 2007;Owens et al, 2008;Buer and Djordjevic, 2009). This observation explains the excess accumulation of anthocyanin in etiolated cop1BBX22-GFPox plants (Fig.…”

The Transcriptional Repressor MYB2 Regulates Both Spatial and Temporal Patterns of Proanthocyandin and Anthocyanin Pigmentation inMedicago truncatula

“…Thus, the central vacuole phenotypes detected in some tt mutants may result from accumulation of toxic upstream intermediates that delay or interrupt vacuole biogenesis. Since unbound PA staining is never observed, it is possible that MATE1 or transport-related proteins comigrate with flavonoids (conjugates) or intermediates in trafficking vesicles to load them into the vesicle rather than the vacuole, and it will be interesting to determine whether PA sequestration in the vacuole is mediated by structures such as anthocyanin vacuolar inclusions (with no membrane envelope) or prevacuolar compartments, as shown for anthocyanins (Zhang et al, 2006;Poustka et al, 2007).…”