Variation of metabolic profiles in developing maize kernels up- and down-regulated for the hda101 gene

UPLC-QTOF-MS metabolomics analysis revealed the contributions of metabolites to the pathogenesis of Rhizoctonia solani strain AG-1-IA

To explore the pathogenesis of Rhizoctonia solani and its phytotoxin phenylacetic acid (PAA) on maize leaves and sheaths, treated leaf and sheath tissues were analyzed and interpreted by ultra-performance liquid chromatography-mass spectrometry combined with chemometrics. The PAA treatment had similar effects to those of R. solani on maize leaves regarding the metabolism of traumatin, phytosphingosine, vitexin 2'' O-beta-D-glucoside, rutin and DIBOA-glucoside, which were up-regulated, while the synthesis of OPC-8:0 and 12-OPDA, precursors for the synthesis of jasmonic acid, a plant defense signaling molecule, was down-regulated under both treatments. However, there were also discrepancies in the influences exhibited by R. solani and PAA as the metabolic concentration of zeaxanthin diglucoside in the R. solani infected leaf group decreased. Conversely, in the PAA-treated leaf group, the synthesis of zeaxanthin diglucoside was enhanced. Moreover, although the synthesis of 12 metabolites were suppressed in both the R. solani- and PAA-treated leaf tissues, the inhibitory effect of R. solani was stronger than that of PAA. An increased expression of quercitrin and quercetin 3-O-glucoside was observed in maize sheaths treated by R. solani, while their concentrations were not changed significantly in the PAA-treated sheaths. Furthermore, a significant decrease in the concentration of L-Glutamate, which plays important roles in plant resistance to necrotrophic pathogens, only occurred in the R. solani-treated sheath tissues. The differentiated metabolite levels may be the partial reason of why maize sheaths were more susceptible to R. solani than leaves and may explain the underlying mechanisms of R. solani pathogenesis.

Metabolic profiling of maize mutants deficient for two glutamine synthetase isoenzymes using 1H-NMR-based metabolomics

INTRODUCTION

Maize mutants deficient for the expression of two genes encoding cytosolic glutamine synthetase (GS) isoenzymes GS1.3 and GS1.4 displayed reduced kernel number and kernel size, respectively, the effect of the mutation being cumulative in the double mutant. However, at maturity, shoot biomass production was not modified in all the mutants, indicating that the reaction catalysed by the enzyme is specifically involved in the control of grain yield.

OBJECTIVE

To examine the physiological impact of the GS mutations on the leaf metabolic profile during the kernel filling period, during which nitrogen is remobilized from the shoots to be further exported to the kernels.

METHODOLOGY

An (1)H-NMR spectroscopy metabolomic was applied to the investigation of metabolic change of the gln1.3, gln1.4 and gln1.3/1.4 double mutant.

RESULTS

In the three GS mutants, an increase in the amount of several N-containing metabolites such as asparagine, alanine, threonine and phophatidylcholine was observed whatever the level of nitrogen fertilisation. In addition, we found an accumulation of phenylalanine and tyrosine, two metabolites involved the primary steps of the phenylpropanoid pathway.

CONCLUSION

Changes in the metabolic profile of the GS mutants suggest that, when cytosolic GS activity is strongly reduced, either alternative metabolic pathways participate in the reassimilation of ammonium released during leaf protein remobilization or that premature leaf senescence is induced when kernel set and kernel filling are affected. The accumulation of phenylalanine and tyrosine in the mutant plants indicates that lignin biosynthesis is altered, thus possibly affecting ear development.

NMR metabolic profiling of transgenic maize with the Cry1Ab gene

The metabolic profiles of seeds from the transgenic maize variety 33P67 and of the corresponding traditional variety were investigated using one- and two-dimensional NMR techniques. The transgenic variety carries a functional Cry1A(b) gene, which confers to the plant the ability to produce Bt insect toxin. About 40 water-soluble metabolites in the maize seed extracts were identified, providing a more complete (1)H and (13)C NMR assignment with respect to the assignment reported in the literature. In particular ethanol, lactic acid, citric acid, lysine, arginine, glycine-betaine, raffinose, trehalose, alpha-galactose, and adenine were identified for the first time in the (1)H NMR spectrum of maize seeds extracts. The (1)H spectra of transgenic and nontransgenic seed maize samples turned out to be conservative, showing the same signals and therefore the same metabolites. However, a higher concentration of ethanol, citric acid, glycine-betaine, trehalose, as well as of another compound not yet completely identified, was observed in the transgenic extracts than in nontransgenic samples. So, it was possible to discriminate between transgenic and nontransgenic metabolic profilings through the use of an appropriate statistical analysis.