A Comprehensive Analysis of Chromoplast Differentiation Reveals Complex Protein Changes Associated with Plastoglobule Biogenesis and Remodeling of Protein Systems in Sweet Orange Flesh

Abstract

(S.X.).Globular and crystalloid chromoplasts were observed to be region specifically formed in sweet orange (Citrus sinensis) flesh and converted from amyloplasts during fruit maturation, which was associated with the composition of specific carotenoids and the expression of carotenogenic genes. Subsequent isobaric tag for relative and absolute quantitation (iTRAQ)-based quantitative proteomic analyses of purified plastids from the flesh during chromoplast differentiation and senescence identified 1,386 putative plastid-localized proteins, 1,016 of which were quantified by spectral counting. The iTRAQ values reflecting the expression abundance of three identified proteins were validated by immunoblotting. Based on iTRAQ data, chromoplastogenesis appeared to be associated with three major protein expression patterns: (1) marked decrease in abundance of the proteins participating in the translation machinery through ribosome assembly; (2) increase in abundance of the proteins involved in terpenoid biosynthesis (including carotenoids), stress responses (redox, ascorbate, and glutathione), and development; and (3) maintenance of the proteins for signaling and DNA and RNA. Interestingly, a strong increase in abundance of several plastoglobule-localized proteins coincided with the formation of plastoglobules in the chromoplast. The proteomic data also showed that stable functioning of protein import, suppression of ribosome assembly, and accumulation of chromoplast proteases are correlated with the amyloplast-to-chromoplast transition; thus, these processes may play a collective role in chromoplast biogenesis and differentiation. By contrast, the chromoplast senescence process was inferred to be associated with significant increases in stress response and energy supply. In conclusion, this comprehensive proteomic study identified many potentially new plastid-localized proteins and provides insights into the potential developmental and molecular mechanisms underlying chromoplast biogenesis, differentiation, and senescence in sweet orange flesh.

Genetics of Pigment Biosynthesis and Degradation

“…Esterification is a common characteristic of floral and ripe fruit carotenoids and may aid the accumulation of the high levels of pigment found in chromoplasts. The formation of the chromoplast may be an essential component of accumulating high levels of carotenoids, and there is substantial evidence of interconnection of the processes of carotenoid biosynthesis and the chloroplast to chromoplast transition in fruit flesh (Li and Yuan 2013;Yuan et al 2015;Zeng et al 2015).…”

Expression Differences of Pigment Structural Genes and Transcription Factors Explain Flesh Coloration in Three Contrasting Kiwifruit Cultivars

“…Chlorophyll, carotenoids and anthocyanins are the most important color pigments of plant tissues, including fruit. In most plant tissues, the bright yellow colors are caused by increases in carotenoid content, such as in pepper ( Guzman et al, 2010 ), carrots ( Clotault et al, 2008 ) and sweet oranges ( Zeng et al, 2015 ). However, for kiwifruit, Montefiori et al (2009b) suggested the yellow color of yellow-fleshed kiwifruit was caused by a disappearance of the chlorophylls, rather than by an increase in the carotenoids.…”

“…Hence, it is speculated that the yellow color formation is controlled by both chlorophyll-related genes and by carotenoid-related genes. Carotenoids also contribute to the red color formation in a few fruit species, typically in red citrus ( Zeng et al, 2015 ), red loquat ( Fu et al, 2012 ) and red pepper ( Tian et al, 2014 ). While for most plants, such as apple, pear and peach, the red color is caused by the presence of anthocyanins ( Telias et al, 2011 ; Wang et al, 2013 ; Zhou et al, 2015 ).…”

Integrating cell biology and proteomic approaches in plants

“…Alteration of ribosomal proteins followed also chromoplast differentiation during orange fruit maturation as found by iTRAQ-based proteomic analysis. Moreover, abundances of carotenoid biosynthetic proteins and plastoglobule-associated proteins coincided with the disappearance of starch granules and emergence of plastoglobules during chromoplast differentiation [60].…”