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Vitamin E, comprising tocopherols and tocotrienols, is a crucial fat-soluble antioxidant that helps maintain intracellular redox homeostasis in plants when they are under stress. Soybeans are a significant source of natural vitamin E. GGDR catalyzes the formation of phytyl diphosphate (PDP), a key vitamin E precursor, and it is involved in chlorophyll degradation. The GmGGDR gene, identified via RNA-seq in soybean germplasms with high and low vitamin E contents, encodes GGDR, a key enzyme involved in both vitamin E synthesis and chlorophyll degradation. This study shows that the GmGGDR-encoded protein is hydrophilic and stable, predominantly expressed in leaves, and markedly responsive to gibberellins. The GmGGDR gene enhances the tolerance of transgenic Arabidopsis and soybean plants to salt and drought stresses; transgenic soybeans overexpressing GmGGDR exhibited an approximately 8-fold increase in POD activity, with no significant changes in SOD and CAT activities. Moreover, the GmGGDR gene enhances the levels of α-, γ-, δ-, and total tocopherol content in transgenic soybean and Arabidopsis plants and also increases the chlorophyll a levels in the leaves of these transgenic plants. The increases in α-tocopherol, γ-tocopherol, and δ-tocopherol and total tocopherol in transgenic Arabidopsis seeds ranged from 177.8% to 600.0%, 42.9% to 90.0%, 17.6% to 292.9%, and 71.4% to 127.3% over the control, respectively. Similarly, transgenic soybeans exhibited a minimum increase of 42.9%, 27.8%, 7.1%, and 25.0% in these tocopherol fractions. Overexpression of GmGGDR also significantly elevated chlorophyll a levels in the leaves of these transgenic plants by 33.3–112.5%. This study preliminarily elucidated the function of the GmGGDR gene. It provides a theoretical foundation for further research. It presents a novel strategy for the genetic enhancement of soybean vitamin E content. Full article

The recycling of metabolic products is a major way to reduce the energy cost of de novo biosynthesis. The salvage pathways involved not only regain a metabolic product but also generate additional molecules that might serve specific physiological, developmental and/or defensive functions. The isoprenoid pathway is a perfect example of a fine-regulated biosynthetic pathway, by virtue of the large number of molecules with different functions that must be synthesized simultaneously. Additionally, isoprenoid salvage pathways have been characterized. Thus, to produce isoprenoid precursors such as farnesyl diphosphate or phytyl diphosphate, short-chain isoprenols recovered from end-chain metabolites are phosphorylated. In the first instance, the so-called FPP-salvage machinery recycles farnesyl diphosphate from proteolyzed farnesylated proteins. In a second example, phytyl diphosphate is recycled from degraded chlorophyll, to be used for the biosynthesis of vitamin E. Both compounds are recovered as alcohols and require two phosphorylation events to be reactivated and reintegrated into the isoprenoid biosynthetic pathway. This review covers current knowledge of isoprenol biosynthesis, metabolism and function, as well as potential benefits of recycling pathways for plants, with a particular focus on stress responses. Full article