Overexpression of lycopene ε-cyclase gene from lycium chinense confers tolerance to chilling stress in Arabidopsis thaliana

GhLCYε-3 characterized as a lycopene cyclase gene responding to drought stress in cotton

Drought stress significantly affects crop productivity. Carotenoids are essential photosynthetic pigment for plants, bacteria, and algae, with signaling and antioxidant functions. Lutein is a crucial branch product in the carotenoid synthesis pathway, which effectively improves the stress tolerance of higher plants. lycopene cyclase, a central enzyme for lutein synthesis, holds great significance in regulating lutein production. This research establishes a correlation between lutein content and stress resistance by measuring the drought resistance and lutein content of various cotton materials. To identify which crucial genes are associated with lutein, the lycopene cyclase family (LCYs) was analyzed. The research found that LCYs form a highly conserved family divided into two subfamilies, LCY-ε (lycopene ε-cyclase) and LCY-β (lycopene β-cyclase). Most members of the LCY family contain photoresponsive elements and abscisic acid elements. qRT-PCR demonstrates showed that most genes responded positively to drought stress, and GhLCYε-3 was expressed significantly differently under drought stress. Virus-induced gene silencing (VIGS) assay showed that the content of GhLCYε-3 was significantly increased with MDA and PRO, and the contents of chlorophyll and lutein were significantly decreased in pYL156 plants. The decrease in GhLCYε-3 expression is speculated to lead to reduced lutein content in vivo, resulting in the accumulation of reactive oxygen species (ROS) and decreased drought tolerance. This research enriched the understanding of LCY gene family and lutein function, and provided a new reference for cotton planting in arid areas.

Synopsis

Lycopene cyclase plays an important role in enhancing the ability of scavenging ROS and drought resistance of plants.

Functional identification of ZDS gene in apple (Malus halliana) and demonstration of it's role in improving saline-alkali stress tolerance

Carotenoids are powerful antioxidants that mediate transfer of electrons, directly affect abiotic stress responses in plants through regulating activity of antioxidant enzymes. ζ-Carotene desaturase (ZDS) is a key enzyme in carotenoid biosynthesis pathway, which can catalyze ζ-carotene to form lycopene to regulate carotenoid biosynthesis and accumulation. However, the mechanism of its regulation of saline-alkali stress remains unclear. In this research, based on transcriptomic analysis of Malus halliana with a apple rootstock, we screened out ZDS gene (LOC103451012), with significantly high expression by saline-alkali stress, whose expression in the leaves was 10.8-fold than that of the control (0 h) under 48 h of stress. Subsequently, the MhZDS gene was isolated from M. halliana, and transgenic Arabidopsis thaliana, tobacco, and apple calli were successfully obtained through agrobacterium-mediated genetic transformation. We found that overexpression of MhZDS enhanced the tolerance of A. thaliana, tobacco and apple calli under saline-alkali stress and caused a variety of physiological and biochemical changes: compared with wild-type, transgenic plants grew better under saline stress and MhZDS-OE lines showed higher chlorophyll content, POD, SOD, CAT activities and proline content, lower electrical conductivity and MDA content. These results indicate that MhZDS plays an important role in plant resistance to saline-alkali stress, providing excellent resistance genes for the regulatory network of salinity stress response in apples and provide a theoretical basis for the breeding of apple varieties with strong saline-alkali resistance.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01333-5.

The maize low-lignin brown midrib3 mutant shows pleiotropic effects on photosynthetic and cell wall metabolisms in response to chilling

Maize (Zea mays L.) is one of the major cereal crops in the world and is highly sensitive to low temperature. Here, changes in photosynthetic and cell wall metabolisms were investigated during a long chilling exposure in inbred line F2 and a low-lignin near-isogenic brown midrib3 mutant (F2bm3), which has a mutation in the caffeic acid O-methyltransferase (COMT) gene. Results revealed that the plant biomass was reduced, and this was more pronounced in F2bm3. Photosynthesis was altered in both lines with distinct changes in photosynthetic pigment content between F2bm3 and F2, indicating an alternative photoprotection mechanism between lines under chilling. Starch remobilization was observed in F2bm3 while concentrations of sucrose, fructose and starch increased in F2, suggesting a reduced sugar partitioning in F2. The cell wall was altered upon chilling, resulting in changes in the composition of glucuronorabinoxylan and a reduced cellulose level in F2. Chilling shifted lignin subunit composition in F2bm3 mutant to a higher proportion of p-hydroxyphenyl (H) units, whereas it resulted in lignin with a higher proportion of syringyl (S) residues in F2. On average, the total cell wall ferulic acid (FA) content increased in both genotypes, with an increase in ether-linked FA in F2bm3, suggesting a greater degree of cross-linking to lignin. The reinforcement of the cell wall with lignin enriched in H-units and a higher concentration in cell-wall-bound FA observed in F2bm3 as a response to chilling, could be a strategy to protect the photosystems.

Heterologous biosynthesis of lutein in S. cerevisiae enabled by temporospatial pathway control

The market-expanding lutein is currently mainly supplied by plant extraction, with microbial fermentation using engineered cell factory emerging as a promising substitution. During construction of lutein-producing yeast, α-carotene formation through asymmetric ε- and β-cyclization of lycopene was found as the main limiting step, attributed to intra-pathway competition of the cyclases for lycopene, forming β-carotene instead. To solve this problem, temperature-responsive expression of β-cyclase was coupled to constitutive expression of ε-cyclase for flux redirection to α-carotene by allowing ε-cyclization to occur first. Meanwhile, the ε-cyclase was engineered and re-localized to the plasma membrane for further flux reinforcement towards α-carotene. Finally, pathway extension with proper combination of carotenoid hydroxylases enabled lutein (438 μg/g dry cells) biosynthesis in S. cerevisiae. The success of heterologous lutein biosynthesis in yeast suggested temporospatial pathway control as a potential strategy in solving intra-pathway competitions, and may also be applicable for promoting the biosynthesis of other natural products.

The gene encoding lycopene epsilon cyclase of celery enhanced lutein and β-carotene contents and confers increased salt tolerance in Arabidopsis

Celery (Apium graveolens L.) is a leafy vegetable of Apiaceae, which is greatly popular because of its rich nutrients. Lutein and β-carotene are two important carotenoids. Lycopene epsilon cyclase (LCY-ε) is a key branch point enzyme in the carotenoid biosynthetic pathway. In this study, we cloned the AgLCY-ε gene from celery and overexpressed it in Arabidopsis. The results showed that both lutein and β-carotene accumulation increased significantly in transgenic Arabidopsis hosting AgLCY-ε gene, compared with wild type (WT) plants. The transcription levels of AtPSY and AtCRTISO genes involved in carotenoids biosynthesis also increased in transgenic lines. One-month-old transgenic Arabidopsis seedlings were treated with 200 mM NaCl. The malondialdehyde (MDA) content in transgenic Arabidopsis plants after salt treatment was significantly lower, and the activities of the two antioxidant enzymes, superoxide dismutase (SOD) and peroxidase (POD), were significantly increased than that of WT plants. Overexpression of AgLCY-ε gene showed increased lutein and β-carotene accumulations, and enhanced salt tolerance in transgenic plants.

A Prunus persica genome-wide RNA-seq approach uncovers major differences in the transcriptome among chilling injury sensitive and non-sensitive varieties

Chilling injury represents a major constrain for crops productivity. Prunus persica, one of the most relevant rosacea crops, have early season varieties that are resistant to chilling injury, in contrast to late season varieties, which display chilling symptoms such as mealiness (dry, sandy fruit mesocarp) after prolonged storage at chilling temperatures. To uncover the molecular processes related to the ability of early varieties to withstand mealiness, postharvest and genome-wide RNA-seq assessments were performed in two early and two late varieties. Differences in juice content and ethylene biosynthesis were detected among early and late season fruits that became mealy after exposed to prolonged chilling. Principal component and data distribution analysis revealed that cold-stored late variety fruit displayed an exacerbated and unique transcriptome profile when compared to any other postharvest condition. A differential expression analysis performed using an empirical Bayes mixture modeling approach followed by co-expression and functional enrichment analysis uncover processes related to ethylene, lipids, cell wall, carotenoids and DNA metabolism, light response, and plastid homeostasis associated to the susceptibility or resistance of P. persica varieties to chilling stress. Several of the genes related to these processes are in quantitative trait loci (QTL) associated to mealiness in P. persica. Together, these analyses exemplify how P. persica can be used as a model for studying chilling stress in plants.

Genetic Engineering of Crypthecodinium cohnii to Increase Growth and Lipid Accumulation

In this study, we evaluated suitable selected markers and optimized transformation protocols to develop a new genetic transformation methodology for DHA-producing Crypthecodinium cohnii. Additionally, ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO), potentially involved in CO₂ fixation under autotrophic conditions, was selected as the target for construction of a gene knockdown mutant. Our results show that the constructs were successfully inserted into the C. cohnii chromosome by homologous recombination. Comparative analysis showed that deletion of the RuBisCO gene promoted cell growth and increased the lipid content of C. cohnii under heterotrophic conditions compared with those of the wild-type. The liquid chromatography-mass spectrometry (LC-MS) based metabolomic analysis showed that the metabolites involved in energy metabolism were upregulated, suggesting that the deletion of the RuBisCO gene may contribute to the re-direction of more carbon or energy toward growth and lipid accumulation under heterotrophic conditions.