In plants, transcriptional regulation is the most important tool for modulating flavonoid biosynthesis. The AtMYB12 gene from Arabidopsis thaliana has been shown to regulate the expression of key enzyme genes involved in flavonoid biosynthesis, leading to the increased accumulation of flavonoids. In this study, the codon-optimized AtMYB12 gene was chemically synthesized. Subcellular localization analysis in onion epidermal cells indicated that AtMYB12 was localized to the nucleus. Its overexpression significantly increased accumulation of flavonoids and enhanced salt and drought tolerance in transgenic Arabidopsis plants. Real-time quantitative PCR (qRT-PCR) analysis showed that overexpression of AtMYB12 resulted in the up-regulation of genes involved in flavonoid biosynthesis, abscisic acid (ABA) biosynthesis, proline biosynthesis, stress responses and ROS scavenging under salt and drought stresses. Further analyses under salt and drought stresses showed significant increases of ABA, proline content, superoxide dismutase (SOD) and peroxidase (POD) activities, as well as significant reduction of H2O2 and malonaldehyde (MDA) content. The results demonstrate the explicit role of AtMYB12 in conferring salt and drought tolerance by increasing the levels of flavonoids and ABA in transgenic Arabidopsis. The AtMYB12 gene has the potential to be used to enhance tolerance to abiotic stresses in plants.

AtMYB12 regulates flavonoids accumulation and abiotic stress tolerance in transgenic Arabidopsis thaliana.

In plants, transcriptional regulation is the most important tool for modulating flavonoid biosynthesis. The basic helix-loop-helix transcription factors are only one example how then flavonoid pathway is regulated. There are other transcription factors as well. In this study, the codon-optimized VvbHLH1 gene from grape was chemically synthesized. Overexpression of VvbHLH1 significantly increased the accumulation of flavonoids and enhanced salt and drought tolerance in transgenic Arabidopsis thaliana plants. Real-time quantitative PCR analysis showed that overexpression of VvbHLH1 resulted in the up-regulation of genes involved in flavonoid biosynthesis, abscisic acid (ABA) signaling pathway, proline biosynthesis, stress responses and ROS scavenging under salt and drought stresses. Further analyses under salt and drought stresses showed significant increases of ABA and proline content, superoxide dismutase and peroxidase activities, as well as significant reduction of hydrogen peroxide (H2O2) and malonaldehyde content. The results demonstrate the explicit role of VvbHLH1 in conferring salt and drought tolerance by increasing the accumulation of flavonoids and ABA signalling in transgenic A. thaliana. The VvbHLH1 gene has the potential to be used to increase the content of valuable flavonoids and improve the tolerance to abiotic stresses in A. thaliana and other plants.

A grape bHLH transcription factor gene, VvbHLH1, increases the accumulation of flavonoids and enhances salt and drought tolerance in transgenic Arabidopsis thaliana

A rapidandconvenient chemical assay fortheenzyme D-glucose 6-phosphateIL-myoinositol 1-phosphate cyclase isdescribed. TheIL-myoinositol 1-phosphate formedenzymically was oxidized withperiodic acidliberating inorganic phosphate, whichwas assayed. myolnositol 2-phosphate can beassayed inthesame way. Glucose 6-phosphate andotherprimaryphosphate esters gave onlyvery small quantities ofinorganic phosphate undertheconditions described. TheKm ofthe enzyme forD-glucose 6-phosphate, 7.5 + 2.5x 10-4M, was identical withthat measuredbytheradiochemical method.2-Deoxy-D-glucose 6-phosphate was a powerful competitive inhibitor, KL2.0 ± 0.5x 10-5 M, butwas notasubstrate forthe enzyme. The enzyme D-glucose 6-phosphate-lL-myoinositol 1-phosphate cyclase hasbeenpartially purified fromyeast(Chen & Charalampous, 1966; Charalampous & Chen,1966), Neurospora (Pina& Tatum,1967), higher plants (VonRuis, Molinari & Hoffinann-Ostenhof, 1967)and animaltissues (Eisenberg, 1967)andsome aspects ofitsmechanismofaction havebeeninvestigated (Barnett & Corina, 1968;Sherman, Stewart& Zinbo,1969). However, further purification andinvestigation of thekinetic properties oftheenzyme havebeen severely hamperedbythelength anddifficulty of theradiochemical assayfortheenzyme, inwhich radioactive D-glucose 6-phosphate isenzymically converted into1L-myoinositol 1-phosphate, which mustthenbeconverted intoinositol andseparated fromcontaminating glucose beforecounting of radioactivity, preferably as the recrystallized hexa-acetate. An alternative assayhasbeenused(Eisenberg, 1967)inwhicha specific phosphatase, inactive towardsD-glucose 6-phosphate, isextracted from rattestes andusedtorelease inorganic phosphate enzymically fromtheIL-myoinositol 1-phosphate. Theinorganic phosphate isthenmeasured. Thispaper describes a rapid andsimple chemical assay fortheinositol phosphate produced bythe cyclase. Themethodcan beusedtoassayother inositol monophosphates.

A Colorimetric Determination ofInositol Monophosphates as an Assay forD-Glucose 6-Phosphate-lL-myoInositol 1-Phosphate Cyclase

Most of the phosphorus in seeds is accumulated in the form of phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate, InsP6). This molecule is a strong chelator of cations important for nutrition, such as iron, zinc, magnesium, and calcium. For this reason, InsP6 is considered an antinutritional factor. In recent years, efforts to biofortify seeds through the generation of low phytic acid (lpa) mutants have been noteworthy. Moreover, genes involved in the biosynthesis and accumulation of this molecule have been isolated and characterized in different species. Beyond its role in phosphorus storage, phytic acid is a very important signaling molecule involved in different regulatory processes during plant development and responses to different stimuli. Consequently, many lpa mutants show different negative pleitotropic effects. The strength of these pleiotropic effects depends on the specific mutated gene, possible functional redundancy, the nature of the mutation, and the spatio-temporal expression of the gene. Breeding programs or transgenic approaches aimed at development of new lpa mutants must take into consideration these different aspects in order to maximize the utility of these mutants.

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Seed Biofortification and Phytic Acid Reduction: A Conflict of Interest for the Plant?

Epidermal bladder cells (EBCs) have been postulated to assist halophytes in coping with saline environments. However, little direct supporting evidence is available. Here, Chenopodium quinoa plants were grown under saline conditions for 5 weeks. One day prior to salinity treatment, EBCs from all leaves and petioles were gently removed by using a soft cosmetic brush and physiological, ionic and metabolic changes in brushed and non-brushed leaves were compared. Gentle removal of EBC neither initiated wound metabolism nor affected the physiology and biochemistry of control-grown plants but did have a pronounced effect on salt-grown plants, resulting in a salt-sensitive phenotype. Of 91 detected metabolites, more than half were significantly affected by salinity. Removal of EBC dramatically modified these metabolic changes, with the biggest differences reported for gamma-aminobutyric acid (GABA), proline, sucrose and inositol, affecting ion transport across cellular membranes (as shown in electrophysiological experiments). This work provides the first direct evidence for a role of EBC in salt tolerance in halophytes and attributes this to (1) a key role of EBC as a salt dump for external sequestration of sodium; (2) improved K+ retention in leaf mesophyll and (3) EBC as a storage space for several metabolites known to modulate plant ionic relations.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/pce.12995

Epidermal bladder cells confer salinity stress tolerance in the halophyte quinoa and Atriplex species

Summary
Myo-inositol-1-phosphate synthase (MIPS) is a key rate limiting enzyme in myo-inositol biosynthesis. The MIPS gene has been shown to improve tolerance to abiotic stresses in several plant species. However, its role in resistance to biotic stresses has not been reported. In this study, we found that expression of the sweet potato IbMIPS1 gene was induced by NaCl, polyethylene glycol (PEG), abscisic acid (ABA) and stem nematodes. Its overexpression significantly enhanced stem nematode resistance as well as salt and drought tolerance in transgenic sweet potato under field conditions. Transcriptome and real-time quantitative PCR analyses showed that overexpression of IbMIPS1 up-regulated the genes involved in inositol biosynthesis, phosphatidylinositol (PI) and ABA signalling pathways, stress responses, photosynthesis and ROS-scavenging system under salt, drought and stem nematode stresses. Inositol, inositol-1,4,5-trisphosphate (IP3), phosphatidic acid (PA), Ca2+, ABA, K+, proline and trehalose content was significantly increased, whereas malonaldehyde (MDA), Na+ and H2O2 content was significantly decreased in the transgenic plants under salt and drought stresses. After stem nematode infection, the significant increase of inositol, IP3, PA, Ca2+, ABA, callose and lignin content and significant reduction of MDA content were found, and a rapid increase of H2O2 levels was observed, peaked at 1 to 2 days and thereafter declined in the transgenic plants. This study indicates that the IbMIPS1 gene has the potential to be used to improve the resistance to biotic and abiotic stresses in plants.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/pbi.12402

Yanyan An

Papers

A myo-inositol-1-phosphate synthase gene, IbMIPS1, enhances salt and drought tolerance and stem nematode resistance in transgenic sweet potato.