Molecular mechanisms underlying carotenogenesis in the chromoplast: multilevel regulation of carotenoid‐associated genes

Abstract

SummaryIn nature, carotenoid function and mode of action are highly determined by the neighboring protein and lipid molecules. Therefore an understanding of the proteins' involvement in carotenoid sequestration would be of great help in elucidating carotenoid function in vivo. Based on a study of the expression of chromoplastspeci®c carotenoid-associated genes from cucumber corolla (CHRC and CHRD), a working model is presented wherein two major regulatory factors control carotenoid sequestration within the chromoplasts: (i)¯oral tissuespeci®c transcriptional regulators of chromoplastogenesis; and (ii) post-transcriptional regulators related to the amount/type of sequestered carotenoids. This model is supported by the major role transcriptional regulation was found to play in the temporal and spatial expression of the CHRC gene, and by the fact that phytohormones such as gibberellic acid (GA 3 ), abscisic acid and ethylene also acted as transcriptional regulators of CHRC expression. The primary response to GA 3 was localized within the CHRC promoter to a 290 bp fragment. Furthermore, we demonstrated strong down-regulation of CHRC expression at post-transcriptional and translational/post-translational levels resulting from inhibition of carotenoid biosynthesis, thus revealing a close link between carotenoid biosynthetic and sequestration machineries.

Protein Profiling of Plastoglobules in Chloroplasts and Chromoplasts. A Surprising Site for Differential Accumulation of Metabolic Enzymes

“…Only one or two proteins belonging to the so-called fibrillin family have been identified in PGs, and these were assigned different names (Pozueta-Romero et al, 1997;Kessler et al, 1999;Vishnevetsky et al, 1999;Langenkamper et al, 2001). The fibrillins were proposed to play a role in stabilizing the globules and preventing their coalescence.…”

Tocopherol Cyclase (VTE1) Localization and Vitamin E Accumulation in Chloroplast Plastoglobule Lipoprotein Particles

“…In addition to membrane-bound compartments, chloroplasts contain lipoprotein particles called plastoglobules. Although a role of plastoglobules in chromoplast differentiation has been defined (1,2), the functions of plastoglobules in chloroplasts are largely unknown. Plastoglobules are associated with thylakoid membranes (3), suggesting that they play a role in thylakoid membrane function.…”

“…Pea plastoglobules contain around a dozen different proteins (3) but so far only members of the plastid lipid-associated protein (PAP) 2 /fibrillin family have been identified (1, 3, 19 -28). At least two PAP/fibrillins were localized at the periphery of plastoglobules (3,26), and purified fibrillin was able to promote carotenoid fibril assembly in vitro (1), suggesting a structural function (29).…”

Expression and Functional Analyses of the Plastid Lipid-Associated Protein CHRC Suggest Its Role in Chromoplastogenesis and Stress

“…In fruit and flower tissues, spatial and temporal expression of these genes is regulated essentially at the transcriptional level. In leaves, their expression under standard greenhouse conditions is very low (Deruere et al, 1994;Chen et al, 1998;Vishnevetsky et al, 1999b). In floral tissue, GA 3 plays a critical role in chromoplastogenesis: It leads to enhanced carotenoid accumulation as well as to transcriptional activation of ChrC expression.…”

“…In floral tissue, GA 3 plays a critical role in chromoplastogenesis: It leads to enhanced carotenoid accumulation as well as to transcriptional activation of ChrC expression. The response to GA was localized to a 290-bp fragment within the ChrC promoter that does not contain known GAresponsive elements (GARE/CARE; Gubler et al, 1999;Vishnevetsky et al, 1999b;Sutoh and Yamauchi, 2003).…”