The Arabidopsis ORANGE (AtOR) gene promotes carotenoid accumulation in transgenic corn hybrids derived from parental lines with limited carotenoid pools

Abstract

The AtOR gene enhances carotenoid levels in corn by promoting the formation of plastoglobuli when the carotenoid pool is limited, but has no further effect when carotenoids are already abundant. The cauliflower orange (or) gene mutation influences carotenoid accumulation in plants by promoting the transition of proplastids into chromoplasts, thus creating intracellular storage compartments that act as metabolic sink. We overexpressed the Arabidopsis OR gene under the control of the endosperm-specific wheat LMW glutenin promoter in a white corn variety that normally accumulates only trace amounts of carotenoids. The total endosperm carotenoid content in the best-performing AtOR transgenic corn line was 32-fold higher than wild-type controls (~25 µg/g DW at 30 days after pollination) but the principal carotenoids remained the same, suggesting that AtOR increases the abundance of existing carotenoids without changing the metabolic composition. We analyzed the expression of endogenous genes representing the carotenoid biosynthesis and MEP pathways, as well as the plastid fusion/translocation factor required for chromoplast formation, but only the DXS1 gene was upregulated in the transgenic corn plants. The line expressing AtOR at the highest level was crossed with four transgenic corn lines expressing different carotenogenic genes and accumulating different carotenoids. The introgression of AtOR increased the carotenoid content of the hybrids when there was a limited carotenoid pool in the parental line, but had no effect when carotenoids were already abundant in the parent. The AtOR gene therefore appears to enhance carotenoid levels by promoting the formation of carotenoid-sequestering plastoglobuli when the carotenoid pool is limited, but has no further effect when carotenoids are already abundant because high levels of carotenoids can induce the formation of carotenoid-sequestering plastoglobuli even in the absence of AtOR.

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

“…ORANGE has been shown as an important genetic tool for carotenoid enhancement in plants (Sun et al ., ; Yuan et al ., 2015b). Ectopic expression of a wild‐type OR leads to carotenoid accumulation in grains of rice and maize (Bai et al ., ; Berman et al ., ), in purple‐fleshed sweetpotato (Park et al ., ) and in calli of sweetpotato and Arabidopsis (Kim et al ., ; Yuan et al ., 2015a). The ‘golden SNP’ in OR is the cause for β‐carotene accumulation in melon fruit (Tzuri et al ., ).…”

Overexpression of the IbOr gene from sweet potato (Ipomea batatas ‘Hoang Long’)in maize increases total carotenoid and β-carotene contents

“…Several reports showed that the overexpression of the Or gene can affect the endogenous carotenoid synthesis genes (Bai et al, 2014(Bai et al, , 2016Goo et al, 2015), while other studies showed that the overexpression of the Or gene stimulates accumulation of carotenoids without an effect on endogenous carotenoid synthesis genes (Yuan et al, 2015;Zhou et al, 2015). Recently, Berman et al (2017) showed that the overexpression of the Or gene depends on the level and composition of carotenoid of the wild-type plants. It was reported that the AtOr gene can enhance carotenoid levels by promoting the formation of carotenoid-sequestering structures when the carotenoid pool is limited, but has no further effect when carotenoids are already abundant (Berman et al, 2017).…”

“…Recently, Berman et al (2017) showed that the overexpression of the Or gene depends on the level and composition of carotenoid of the wild-type plants. It was reported that the AtOr gene can enhance carotenoid levels by promoting the formation of carotenoid-sequestering structures when the carotenoid pool is limited, but has no further effect when carotenoids are already abundant (Berman et al, 2017). Our results showed that in all transgenic plants derived from wildtype maize with less carotenoid content (H145-WT), the content of both total carotenoids and β-carotene was higher than in transgenic plants from wild-type maize with more carotenoid content (H95-WT).…”

“…This protects the stability of IbPSY protein and leads to carotenoid accumulation. The different expression manners of the Or gene have led to varied phenomena: changing both the content and the composition of carotenoids (Lopez et al, 2008), promoting the accumulation of β-carotene and other carotenoids (Lopez et al, 2008;Li et al, 2012), and increasing the total carotenoid content without affecting the composition of carotenoids (Goo et al, 2015;Berman et al, 2017). In our work, the overexpression of the IbOr gene from yellow-fleshed sweet potato cultivar Hoang Long in transgenic maize plants resulted in the increase of both total carotenoids (1.76-10.36-fold) and β-carotene (2.03-15.11-fold).…”

“…The overexpression of the Or gene from Ipomea batatas (IbOr) in transgenic plants of potato, alfalfa, and sweet potato (Li et al, 2012;Goo et al, 2015;Park et al, 2015;Wang et al, 2015;Cho et al, 2016) has led to increased carotenoid accumulation without affecting carotenoid synthesis. A recent report on the role of the Arabidopsis thaliana Or gene (AtOr) in transgenic white maize and their hybrids (Berman et al, 2017) suggested the potential use of the Or gene to improve the carotenoid content of staple crops including maize.…”