Orange protein has a role in phytoene synthase stabilization in sweetpotato

Abstract

Carotenoids have essential roles in light-harvesting processes and protecting the photosynthetic machinery from photo-oxidative damage. Phytoene synthase (PSY) and Orange (Or) are key plant proteins for carotenoid biosynthesis and accumulation. We previously isolated the sweetpotato (Ipomoea batatas) Or gene (IbOr), which is involved in carotenoid accumulation and salt stress tolerance. The molecular mechanism underlying IbOr regulation of carotenoid accumulation was unknown. Here, we show that IbOr has an essential role in regulating IbPSY stability via its holdase chaperone activity both in vitro and in vivo. This protection results in carotenoid accumulation and abiotic stress tolerance. IbOr transcript levels increase in sweetpotato stem, root, and calli after exposure to heat stress. IbOr is localized in the nucleus and chloroplasts, but interacts with IbPSY only in chloroplasts. After exposure to heat stress, IbOr predominantly localizes in chloroplasts. IbOr overexpression in transgenic sweetpotato and Arabidopsis conferred enhanced tolerance to heat and oxidative stress. These results indicate that IbOr holdase chaperone activity protects IbPSY stability, which leads to carotenoid accumulation, and confers enhanced heat and oxidative stress tolerance in plants. This study provides evidence that IbOr functions as a molecular chaperone, and suggests a novel mechanism regulating carotenoid accumulation and stress tolerance in plants.

IbOr Regulates Photosynthesis under Heat Stress by Stabilizing IbPsbP in Sweetpotato

“…To investigate the expression of IbPsbP, 1-month-old sweetpotato plants with six fully expanded leaves were subjected to various stresses [38 and 47°C (heat), 4°C (cold), 100 mM methyl viologen (MV), 10 mM H 2 O 2 , and 200 mM NaCl] (Kim et al, 2014; Park et al, 2016), and then samples were taken from the fully expanded leaves third from the top of treated plants at the indicated time. Two-month-old sweetpotato plants were used for acquisition of samples of leaves from shoot apical meristem, according to position-dependent development stage (Ji et al, 2016).…”

Ectopic expression of ORANGE promotes carotenoid accumulation and fruit development in tomato

“…OR encodes a plastidial DnaJ cysteine‐rich domain‐containing protein and is highly conserved among plant species (Lu et al ., ; Tzuri et al ., ). Recent studies reveal that OR has dual roles in post‐transcriptionally regulating PSY and promoting chromoplast biogenesis for carotenoid accumulation in plants (Chayut et al ., ; Park et al ., ; Welsch et al ., ; Yuan et al ., 2015a; Zhou et al ., ). Expression of a wild‐type OR ( OR WT ) results in carotenoid accumulation in multiple plant species (Bai et al ., ; Berman et al ., ; Park et al ., ; Yuan et al ., 2015a), likely due to its role in regulating PSY activity.…”

A kiwifruit (Actinidia deliciosa) R2R3‐MYB transcription factor modulates chlorophyll and carotenoid accumulation

“…The tissue-specific expression observed between different PSYs in these species suggests a tightly regulated transcription of this step. The PSY step is also post-transcriptionally regulated by OR/OR-like proteins affecting PSY protein levels and carotenoid content in Arabidopsis and sweet potato without affecting PSY transcript levels (Zhou et al, 2015;Park et al, 2016). Recently, it has been reported that the OR protein, with the golden SNP mutation, may increase carotenoid content by negatively regulating the downstream beta-carotene hydroxylase activity in melon (Chayut et al, 2017).…”