Effect of Overexpression of γ-Tocopherol Methyltransferase on α-Tocopherol and Fatty Acid Accumulation and Tolerance to Salt Stress during Seed Germination in Brassica napus L

Rapeseed (Brassica napus L.) is an important oil crop and a major source of tocopherols, also known as vitamin E, in human nutrition. Enhancing the quality and composition of fatty acids (FAs) and tocopherols in seeds has long been a target for rapeseed breeding. The gene γ-Tocopherol methyltransferase (γ-TMT) encodes an enzyme catalysing the conversion of γ-tocopherol to α-tocopherol, which has the highest biological activity. However, the genetic basis of γ-TMT in B. napus seeds remains unclear. In the present study, BnaC02.TMT.a, one paralogue of Brassica napus γ-TMT, was isolated from the B. napus cultivar "Zhongshuang11" by nested PCR, and two homozygous transgenic overexpression lines were further characterised. Our results demonstrated that the overexpression of BnaC02.TMT.a mediated an increase in the α- and total tocopherol content in transgenic B. napus seeds. Interestingly, the FA composition was also altered in the transgenic plants; a reduction in the levels of oleic acid and an increase in the levels of linoleic acid and linolenic acid were observed. Consistently, BnaC02.TMT.a promoted the expression of BnFAD2 and BnFAD3, which are involved in the biosynthesis of polyunsaturated fatty acids during seed development. In addition, BnaC02.TMT.a enhanced the tolerance to salt stress by scavenging reactive oxygen species (ROS) during seed germination in B. napus. Our results suggest that BnaC02.TMT.a could affect the tocopherol content and FA composition and play a positive role in regulating the rapeseed response to salt stress by modulating the ROS scavenging system. This study broadens our understanding of the function of the Bnγ-TMT gene and provides a novel strategy for genetic engineering in rapeseed breeding.

Biochemical and molecular insights of PGPR application for the augmentation of carotenoids, tocopherols, and folate in the foliage of Moringa oleifera

Plant Growth Promoting Rhizobacteria (PGPR) were utilized to contemplate their impact on the foliage of Moringa oleifera and examined for changes in tocopherols, chlorophyll, carotenoids, and folate in the sixth week. Among the eight treatments, Bacillus subtilis GB03, B. pumilus SE34, B. pumilus T4, and Pseudomonas fluorescens UOM14 improved α-tocopherol (10-14 fold) and β-carotene (1-1.40 fold) altogether significantly (P ≤ 0.05). The most significant improvement in folate content was apparent for B. subtilis IN937B (5.47 fold) trailed by B. pumilus SE34 (5.05 fold) and B. pumilus T4 (5.12 fold) treatments. P. fluorescens UOM14 indicated remarkable improvement in Chl a (0.39 fold) and Chl b (0.44 fold) content. Organisms showing a significant increase for the analyzed molecules in individual treatment were blended in different combinations and were used for the next set of treatments. Of all the three combinations, Combination 2 (COM2-B. pumilus SE34 + B. pumilus T₄ + B. pumilus INR7) showed the maximum increase in α-tocopherol (8.46 fold) and γ-tocopherol (8.45 fold), followed by Combination 3 (COM3-B. pumilus SE34 + B. pumilus T₄ + P. fluorescens UOM14) (5.93 and 3.65 fold). On the whole COM2 containing different strains of B. pumilus was found to enhance the targeted metabolites in foliage significantly. Real-time PCR studies were conducted for the biochemical pathway genes of the targeted molecules, including, γ-tocopherol methyltransferase (γ-TMT), phytoene synthase (PSY), phytoene desaturase (PDS), lycopene β cyclase (LBC) and dihydrofolate reductase thymidylate synthase (DHFR-TS). All the selected genes exhibited an up-regulation compared to control, similar to the biochemical output. Our investigation provides the strong evidence that PGPR can be viably utilized in combination to enhance the quality of the food crops.

Molecular cloning and functional analysis of the promoter of γ-Tocopherol Methyl Transferase (γ-TMT) gene of soybean (Glycine max)

γ-Tocopherol methyl transferase (γ-TMT) (EC 2.1.1.95) is the key enzyme of the tocopherol biosynthetic pathway that determines the α-tocopherol concentration in plants. The overexpression of γ-TMT has been a successful approach for α-tocopherol enrichment of most plants including soybean. The typical soybean varieties are rich in γ-tocopherol (constitutes nearly 65-70% of its total seed tocopherol pool), while α-tocopherol, the biologically most active form among all tocopherols, constitutes only 10% of the total tocopherol content. The identification of soybean varieties that have seed α-tocopherol as high as > 20% of the total tocopherols has shifted attention towards the breeding based approach for α-tocopherol enrichment of this crop. Previous research on this aspect suggests that polymorphisms in γ-TMT promoter might be associated with the high α-tocopherol concentration of some soybean varieties. To understand the molecular basis of genetic variation for α-tocopherol concentration in Indian varieties of soybean we cloned the 1.4 kb upstream promoter region of γ-TMT from a high α-tocopherol containing soybean variety (Bragg) as well as from a low α-tocopherol containing variety (DS 2706). Cloning of each of these promoters in pORE R2 vector having GUS reporter gene and the subsequent GUS assay revealed a slightly high promoter activity of Bragg γ-TMT as compared to DS 2706 γ-TMT. On promoter sequence analysis, no sequence polymorphisms were observed in the core promoter region of this gene. However, seven single nucleotide polymorphisms (SNPs) were observed outside the core promoter region. Further study based on deletion construct analysis of this promoter will elucidate the significance of these SNPs in influencing the activity of γ-TMT promoter and the α-tocopherol concentration.

Identification of differentially-expressed genes potentially implicated in drought response in pitaya (Hylocereus undatus) by suppression subtractive hybridization and cDNA microarray analysis

Drought is one of the most severe threats to the growth, development and yield of plant. In order to unravel the molecular basis underlying the high tolerance of pitaya (Hylocereus undatus) to drought stress, suppression subtractive hybridization (SSH) and cDNA microarray approaches were firstly combined to identify the potential important or novel genes involved in the plant responses to drought stress. The forward (drought over drought-free) and reverse (drought-free over drought) suppression subtractive cDNA libraries were constructed using in vitro shoots of cultivar 'Zihonglong' exposed to drought stress and drought-free (control). A total of 2112 clones, among which half were from either forward or reverse SSH library, were randomly picked up to construct a pitaya cDNA microarray. Microarray analysis was carried out to verify the expression fluctuations of this set of clones upon drought treatment compared with the controls. A total of 309 expressed sequence tags (ESTs), 153 from forward library and 156 from reverse library, were obtained, and 138 unique ESTs were identified after sequencing by clustering and blast analyses, which included genes that had been previously reported as responsive to water stress as well as some functionally unknown genes. Thirty six genes were mapped to 47 KEGG pathways, including carbohydrate metabolism, lipid metabolism, energy metabolism, nucleotide metabolism, and amino acid metabolism of pitaya. Expression analysis of the selected ESTs by reverse transcriptase polymerase chain reaction (RT-PCR) corroborated the results of differential screening. Moreover, time-course expression patterns of these selected ESTs further confirmed that they were closely responsive to drought treatment. Among the differentially expressed genes (DEGs), many are related to stress tolerances including drought tolerance. Thereby, the mechanism of drought tolerance of this pitaya genotype is a very complex physiological and biochemical process, in which multiple metabolism pathways and many genes were implicated. The data gained herein provide an insight into the mechanism underlying the drought stress tolerance of pitaya, as well as may facilitate the screening of candidate genes for drought tolerance.