Several environmental factors adversely affect plant growth and development and final yield performance of a crop. Drought, salinity, nutrient imbalances (including mineral toxicities and deficiencies) and extremes of temperature are among the major environmental constraints to crop productivity worldwide. Development of crop plants with stress tolerance, however, requires, among others, knowledge of the physiological mechanisms and genetic controls of the contributing traits at different plant developmental stages. In the past two decades, biotechnology research has provided considerable insights into the mechanism of biotic stress tolerance in plants at the molecular level. Furthermore, different abiotic stress factors may provoke osmotic stress, oxidative stress and protein denaturation in plants, which lead to similar cellular adaptive responses such as accumulation of compatible solutes, induction of stress proteins, and acceleration of reactive oxygen species scavenging systems. Recently, various methods are adapted to improve plant tolerance to salinity injury through either chemical treatments (plant hormones, minerals, amino acids, quaternary ammonium compounds, polyamines and vitamins) or biofertilizers treatments (Asymbiotic nitrogen-fixing bacteria, symbiotic nitrogen-fixing bacteria) or enhanced a process used naturally by plants (mycorrhiza) to minimise the movement of Na+ to the shoot. Proper management of Arbuscular Mycorrhizal Fungi (AMF) has the potential to improve the profitability and sustainability of salt tolerance. In this review article, the discussion is restricted to the mycorrhizal symbiosis and alleviation of salinity stress.

Phthalate, a plasticizer, endocrine disruptor, and potential carcinogen, is degraded by a variety of bacteria. This degradation is initiated by phthalate dioxygenase (PDO), a Rieske oxygenase (RO) that catalyzes the dihydroxylation of phthalate to a dihydrodiol. PDO has long served as a model for understanding ROs despite a lack of structural data. Here we purified PDO KF1 from Comamonas testosteroni KF1 and found that it had an apparent k cat / K m for phthalate of 0.58 ± 0.09 μM −1 s −1 , over 25-fold greater than for terephthalate. The crystal structure of the enzyme at 2.1 Å resolution revealed that it is a hexamer comprising two stacked α 3 trimers, a configuration not previously observed in RO crystal structures. We show that within each trimer, the protomers adopt a head-to-tail configuration typical of ROs. The stacking of the trimers is stabilized by two extended helices, which make the catalytic domain of PDO KF1 larger than that of other characterized ROs. Complexes of PDO KF1 with phthalate and terephthalate revealed that Arg207 and Arg244, two residues on one face of the active site, position these substrates for regiospecific hydroxylation. Consistent with their roles as determinants of substrate specificity, substitution of either residue with alanine yielded variants that did not detectably turnover phthalate. Together, these results provide critical insights into a pollutant-degrading enzyme that has served as a paradigm for ROs and facilitate the engineering of this enzyme for bioremediation and biocatalytic applications.

on linseed (Linum usitatissimum L.) growth response with phosphate solubilizing bacteria Pseudomonas fluorescens; different doses of superphosphate were used: 20 kg ha -1 (half recommended dose), 40 kg ha -1 (recommended dose), and 80 kg ha -1 (double recommended dose) in earthen pots filled with sterilized soil under greenhouse conditions. Among all the growth parameters, the following were the highest in the G. mosseae + P. fluorescens combination at the medium concentration (recommended superphosphate dose): plant height (78.74 ± 1.8 cm), fresh shoot weight (3.45 ± 0.294 g), dry shoot weight (0.57 ± 0.007 g), fresh root weight (0.223 ± 0.023 g), dry root weight (0.036 ± 0.004 g), root length (17.67 ± 0.48 cm), AM spore number (94.4 ± 9.86), shoot (1.14 ± 0.115%) and root (1.29 ± 0.110%) P content, and acidic (0.447 ± 0.012 IU g -1 FW) and alkaline phosphatase activity (0.119 ± 0.008 IU g -1 FW). The percentage mycorrhizal root colonization with the A. laevis + P. fluorescens (86.86 ± 2.17%) combination and chlorophyll content with the G. mosseae + A. laevis + P. fluorescens (0.474 ± 0.009 mg g -1 FW) combination recorded the highest values at the low concentration (half recommended superphosphate dose) as compared with non-mycorrhizal plants (control). The high superphosphate dose clearly reduced or decreased all the growth parameters. Therefore, vigorous growth and maximum flax yield can be achieved by inoculating plants with AM fungi and P. fluorescens with the recommended dose or less than the recommended dose of superphosphate.

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Chlorogenic acid (CGA) is a phenolic compound with well-known antibacterial properties against pathogens. In this study, structural and biochemical characterization display the inhibitory role of CGA against the enzyme of the shikimate pathway, a well characterized drug target in several pathogens. Here, we report the crystal structures of dehydroquinate synthase (DHQS), the second enzyme of the shikimate pathway, from Providencia alcalifaciens (PaDHQS), in binary complex with NAD and ternary complex with NAD and CGA. Structural analyses reveal that CGA occupies the substrate position in the active site of PaDHQS, which disables domain movements, leaving the enzyme in open and catalysis incompetent state. The binding analyses by ITC and SPR show that CGA binds to PaDHQS with a KD value of 6.3 μM and 0.5 μM respectively. In vitro enzyme inhibition studies show that CGA inhibits PaDHQS with a Ki of 235 ± 21 μM; while it inhibits the growth of Providencia alcalifaciens, Moraxella catarrhalis, Staphylococcus aureus and Escherichia coli with MIC values of 60 to 100 μM. In the presence of aromatic amino acids supplied externally, CGA doesn't show the toxic effect. These results, along with the observations of the inhibition of DAHP regulatory domain by CGA in our previous study, suggest that CGA binds to shikimate pathway enzymes with high affinity and inhibits their catalysis, and can be further exploited for designing novel drug-like molecules. Importance The shikimate pathway is an attractive target for the development of herbicides and antimicrobial agents as it is essential in plants, bacteria and apicomplexan parasites, but absent in humans. The enzymes of shikimate pathway are conserved among bacteria. Thus, the inhibitors of the shikimate pathway will act on wide range of pathogens. We have identified that chlorogenic acid targets the enzymes of shikimate pathway. The crystal structure of dehydroquinate synthase the second enzyme of the pathway, in complex with chlorogenic acid and enzymatic inhibition studies explain the mechanism of inhibition of chlorogenic acid. These results suggest that chlorogenic acid has a good chemical scaffold and have important implications for the further development as potent inhibitor of shikimate pathway enzymes.