Lycopene β-cyclase expression influences plant physiology, development, and metabolism in tobacco plants

Abstract

Carotenoids are important isoprenoids produced in the plastids of photosynthetic organisms that play key roles in photoprotection and antioxidative processes. β-carotene is generated from lycopene by the lycopene β-cyclase (LCYB). Previously, we demonstrated that the introduction of the Daucus carota (carrot) DcLCYB1 gene into tobacco (cultivar Xanthi) resulted in increased levels of abscisic acid (ABA) and especially gibberellins (GAs), resulting in increased plant yield. In order to understand this phenomenon prior exporting this genetic strategy to crops, we generated tobacco (cultivar Petit Havana) mutants that exhibited a wide range of LCYB expression. Transplastomic plants expressing DcLCYB1 at high levels showed a wild-type-like growth, even though their pigment content was increased, and their leaf GA content was reduced. RNAi NtLCYB lines showed different reductions in NtLCYB transcript abundance, correlating with reduced pigment content and plant variegation. Photosynthesis (leaf absorptance, Fv/Fm, and ETRII) and plant growth were impaired. Remarkably, drastic changes in phytohormone content also occurred in the RNAi lines. However, external application of phytohormones was not sufficient to rescue their phenotypes, suggesting that altered photosynthetic efficiency might be another important factor explaining their reduced biomass. These results show that LCYB expression influences plant biomass by different mechanisms and suggests thresholds for LCYB expression levels that might be beneficial/detrimental for plant growth.

Metabolic Engineering for Efficient Ketocarotenoid Accumulation in the Green Microalga Chlamydomonas reinhardtii

“…Two competing lycopene cyclases (LCYB and LCYE) balance the proportion of α- and ß-carotene after the cyclization of lycopene to contain ε-β or β-ionone-type end groups, respectively. In plants, flux toward ß-carotene can be enhanced by LCYB overexpression, which results in increased biomass, carotenoid contents, and improved stress tolerance − partially due to the deregulation of abscisic acid (ABA) biosynthesis and regulatory feedback effects. Hydroxylation and ketolation steps, involving the ß-carotene hydroxylase (CHYB) and ß-carotene ketolase (BKT), complete astaxanthin biosynthesis from ß-carotene. , In C.…”

Farnesyl pyrophosphate compartmentalization in the green microalga Chlamydomonas reinhardtii during heterologous (E)-α-bisabolene production

“…overexpression of 1-deoxy- d -xylulose-5-phosphate synthase) [ 6 ], or metabolic pull through modification of carotenoid biosynthesis (i.e. lycopene cyclase [ 30 , 31 ]). Importantly, the strategies developed here can be applied to the production of any sesquiterpenoid, including compounds of higher value with more realistic economic potential than the biofuel precursor bisabolene.…”

Are carotenoids the true colors of crop improvement?

“…In summary, increasing LCYB expression and b-carotene content can trigger the emergence of a series of beneficial phenotypes by modulating the content of hormones, growth regulators, and osmoprotectants in tobacco and tomato (Moreno et al, 2020(Moreno et al, , 2021aKossler et al, 2021;Mi et al, 2022). Besides being a tool for provitamin A biofortification, the effect of constitutive overexpression of LCYB on the composition of bioactive metabolites revealed a promising alternative for improving crop productivity and resilience.…”