A single amino acid substitution in an ORANGE protein promotes carotenoid overaccumulation in arabidopsis

Authors: YUAN, HUI - Cornell University; OWSIANG, KATHERIN - Cornell University; SHEEJA, TE - Cornell University; ZHOU, XIANGJUN - Cornell University; RODRIGUEZ, CAROLINE - Cornell University; LI, YONGXI - Huazhong Agricultural University; WELSCH, RALF - University Of Freiburg; CHAYUT, NOAM - Agricultural Research Organization Of Israel; Yang, Yong; Thannhauser, Theodore - Ted; PATHASARATHY, MANDAYAM - Cornell University; XU, QIANG - Huazhong Agricultural University; DENG, XIUXIN - Huazhong Agricultural University; FEI, ZHANGJUN - Cornell University; SCHAFFER, ARTHUR - Agricultural Research Organization, Volcani Center; KATZIR, NURIT - Agricultural Research Organization Of Israel; BURGER, JOSEPH - Agricultural Research Organization Of Israel; TADMOR, YAAKOV - Agricultural Research Organization Of Israel; Li, Li

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2015
Publication Date: 9/4/2014
Citation: Yuan, H., Owsiang, K., Sheeja, T., Zhou, X., Rodriguez, C., Li, Y., Welsch, R., Chayut, N., Yang, Y., Thannhauser, T.W., Pathasarathy, M.V., Xu, Q., Deng, X., Fei, Z., Schaffer, A., Katzir, N., Burger, J., Tadmor, Y., Li, L. 2014. A single amino acid substitution in an ORANGE protein promotes carotenoid overaccumulation in arabidopsis. Plant Physiology. 169(1):421-431.

Interpretive Summary: Carotenoids are indispensable to plant growth and human health. To develop crops with enhanced nutritional quality, it is essential to find right genetic tools effective in promoting carotenoid accumulation. In this study, we discover that alteration of a single amino acid in a wild type ORANGE (OR) protein greatly enhances its ability to promote carotenoid accumulation. The basis behind this was found to be due to its ability to regulate the key rate-limiting enzyme in carotenoid biosynthesis pathway and to modulate metabolic storage sink formation. Our findings establish that it is possible to generate functional alleles of the OR gene in any crops and use them as powerful tools for agricultural products biofortification with pro-vitamin A for enhanced crop nutritional value.

Technical Abstract: Carotenoids are crucial for plant growth and human health. The finding of ORANGE (OR) protein as a pivotal regulator of carotenogenesis offers a unique opportunity to comprehensively understand the regulatory mechanisms of carotenoid accumulation and develop crops with enhanced nutritional quality. Here we demonstrated that alteration of a single amino acid in wild type OR greatly enhanced its ability to promote carotenoid accumulation. While overexpression of OR from Arabidopsis (AtOR) or from an agronomically important crop sorghum (SbOR) increased carotenoid levels up to two-fold, expression of AtORHis (R90H) or SbORHis (R104H) variants dramatically enhanced carotenoid accumulation by up to seven-fold in the Arabidopsis calli. Moreover, we found that AtORAla (R90A) functioned similarly as AtORHis to promote carotenoid overproduction. Neither AtOR nor AtORHis greatly affected carotenogenic gene expression. AtORHis exhibited similar interactions with phytoene synthase (PSY) as AtOR in post-transcriptionally regulating PSY protein abundance, but was not accompanied/linked with enhanced PSY activity. AtORHis triggered biogenesis of membranous chromoplasts in the Arabidopsis calli, which shared similar structures as chromoplasts found in curd of orange cauliflower mutant. By contrast, AtOR did not cause plastid type change in comparison with wild type, but produced plastids containing larger electron dense plastoglobuli. The unique ability of AtORHis in mediating chromoplast biogenesis is responsible for its enhanced carotenoid overproduction. Our study demonstrates ORHis/Ala as powerful tools for carotenoid enrichment in plants, and provides insights into the mechanisms underlying ORHis regulated carotenoid accumulation.