Characterization and functional analysis of phytoene synthase gene family in tobacco

Background Carotenoids play important roles in photosynthesis, hormone signaling, and secondary metabolism. Phytoene synthase (PSY) catalyzes the first step of the carotenoid biosynthetic pathway. In this study, we aimed to characterize the PSY genes in tobacco and analyze their function. Results In this study, we identified three groups of PSY genes, namely PSY1, PSY2, and PSY3, in four Nicotiana species; phylogenetic analysis indicated that these genes shared a high similarity with those in tomato but not with those in monocots such as rice and maize. The expression levels of PSY1 and PSY2 were observed to be highest in leaves compared to other tissues, and they could be elevated by treatment with certain phytohormones and exposure to strong light. No PSY3 expression was detected under these conditions. We constructed virus-induced PSY1 and PSY2 silencing in tobacco and found that the newly emerged leaves in these plants were characterized by severe bleaching and markedly decreased carotenoid and chlorophyll content. Thylakoid membrane protein complex levels in the gene-silenced plants were also less than those in the control plants. The chlorophyll fluorescence parameters such as Fv/Fm, ΦPSII, qP, and NPQ, which reflect photosynthetic system activities, of the gene-silenced plants were also significantly decreased. We further performed RNA-Seq and metabonomics analysis between gene-silenced tobacco and control plants. RNA-Seq results showed that abiotic stress, isoprenoid compounds, and amino acid catabolic processes were upregulated, whereas the biosynthesis of cell wall components was downregulated. Metabolic analysis results were consistent with the RNA-Seq. We also found the downstream genes in carotenoid biosynthesis pathways were upregulated, and putative transcription factors that regulate carotenoid biosynthesis were identified. Conclusions Our results suggest that PSY can regulate carotenoid contents not only by controlling the first biosynthesis step but also by exerting effects on the expression of downstream genes, which would thereby affect photosynthetic activity. Meanwhile, PSY may affect other processes such as amino acid catabolism and cell wall organization. The information we report here may aid further research on PSY genes and carotenoid biosynthesis.

Current Status and Future Perspectives of Biofortification in Wheat

Wheat is the main cereal crop worldwide and about 2 billion people suffer from Zn and Fe deficiency because of their dependence just on cereal crops. Three Billion people are malnourished suffering from mild to severe physical and mental disabilities. Vast genetic diversity of Wheat exists in nature that differs in their mineral compositions. Main deficient micronutrients are Provitamin-A, Zn & Fe which deficiencies cause serious physical and mental abnormalities. Different methods of enhancing mineral contents of plants products have been used, out of which biofortification has proved more promising and economical. Bacterial phytoene synthase gene (crtb) and carotene desaturase gene (crti) has been transferred in wheat that has increased carotenoid content but darker colour has less public acceptance.GPC-B1 gene is found to be associated with increase micronutrients but it lowers the overall yield of the plant. Several new methodologies such as oligo-directed mutagenesis, reverse breeding, RNA directed DNA methylation and genome editing have been used for increasing micronutrient composition and their bioavailability. But the combination of Plant Breeding methods with Molecular Techniques will be more useful for advancement in this field.