Effect of the cauliflower Or transgene on carotenoid accumulation and chromoplast formation in transgenic potato tubers

Abstract

Transgenic plants have facilitated our understanding of the functional roles of genes and the metabolic processes affected in plants. Recently, the Or gene was isolated from an orange cauliflower mutant and it was shown that the Or gene could serve as a novel genetic tool to enrich carotenoid content in transgenic potato tubers. An in-depth characterization of these Or transgenic lines is presented here. It was found that the Or transgene may facilitate the identification of potential rate-limiting step(s) of the carotenoid biosynthetic pathway. The Or transgenic tubers accumulated not only increased levels of carotenoids that normally are present in the controls, but also three additional metabolite intermediates of phytoene, phytofluene, and zeta-carotene, indicating that the desaturation steps became limiting following the expression of the Or transgene. Moreover, we observed that long-term cold storage greatly enhanced carotenoid content in the Or transgenic tubers to a level of 10-fold over controls. Expression of the Or transgene in the transgenic plants caused no dramatic changes in the transcript levels of the endogenous carotenoid biosynthetic genes, which is in agreement with the Or gene not directly controlling carotenoid biosynthesis. Microscope analysis revealed that the Or transgene conferred the formation of chromoplasts containing carotenoid sequestering structures in a heterologous system. Such structures were not observed in tubers of potato cultivars that accumulate high levels of carotenoids. Collectively, these results provide direct evidence demonstrating that the Or gene indeed controls chromoplast differentiation and that regulation of chromoplast formation can have a profound effect on carotenoid accumulation in plants.

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

“…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).…”

Transgenic Pro-Vitamin A Biofortified Crops for Improving Vitamin A Deficiency and Their Challenges

“…Chromoplast biogenesis, therefore, can be part of a strategy to enhance pVA contents and their stability [51]. Expression of the cauliflower Or gene was investigated for carotenoid accumulation and stability in potato [51,63]. Transgenic potato tubers enhanced carotenoids and β-carotene, and continued accumulating them during long-term cold storage with induced formation of chromoplasts [63].…”

Application of Plant Biotechnology Techniques in Antioxidant Production

“…The Or gene product is a protein, DnaJ which contains a cysteine-rich domain. It is interesting that the DnaJ transcription factor does not increase the level of carotenoids by stimulating endogenous biosynthesis, but by affecting the formation of isolated structures within the hromoplast in which carotenoids have been accumulated (Lu et al, 2006;Lopez et al, 2008;Sanghera et al, 2013).…”