Genome-Wide Analysis of Genes Involved in the GA Signal Transduction Pathway in ‘duli’ Pear (Pyrus betulifolia Bunge)

Gibberellic acid (GA) is an important phytohormone that regulates every aspect of plant growth and development. While elements involved in GA signaling have been identified and, hence, their functions have been well studied in model plants, such as Arabidopsis and rice, very little is known in pear. We, therefore, analyzed the genes related to GA signaling from the recently sequenced genome of the wildtype ‘duli’ pear (Pyrus betulifolia Bunge), a widely used rootstock for grafting in pear cultivation in China due to its vigorous growth and resistance to abiotic and biotic stress. In total, 15 genes were identified, including five GA receptors PbGID1s (GA-INSENSTIVE DWARF 1), six GA negative regulators, PbDELLAs, and four GA positive regulators, PbSLYs. Exogenous application of GA could promote the expression of PbGID1s but inhibit that of PbDELLAs and PbSLYs in tissue culture ‘duli’ pear seedlings. The expression profiles of these genes in field-grown trees under normal growth conditions, as well as in tissue-cultured seedlings treated with auxin (IAA), GA, paclobutrazol (PAC), abscisic acid (ABA), and sodium chloride (NaCl), were also studied, providing further evidence of the involvement of these genes in GA signaling in ‘duli’ pear plants. The preliminary results obtained in this report lay a good foundation for future research into GA signaling pathways in pear. Importantly, the identification and preliminary functional verification of these genes could guide molecular breeding in order to obtain the highly desired dwarf pear rootstocks for high-density plantation to aid easy orchard management and high yielding of pear fruits.     

Unusual Effect of α-olefins as Chain Transfer Agents in Ethylene Polymerization over the Catalyst with Nonsymmetrical Bis(imino)pyridine Complex of Fe(II) and Modified Methylalumoxane (MMAO) Cocatalyst

Ethylene polymerization with bis(imino)pyridlyiron precatalysts generally produces linear polyethylene (PE) even with the presence of α-olefins because α-olefins are not incorporated into polymeric products. Interestingly, α-olefins, such as hexene-1 or butene-1, have been found to act as effective chain transfer agents in the ethylene polymerization promoted by nonsymmetrical bis(imino)pyridyliron complexes with modified methylalumoxane (MMAO), resulting in higher catalytic activities with higher amounts of polymers with lower molecular weights, and, more importantly, narrower molecular weight distributions of the resultant polyethylenes (PE). This phenomenon confirms the assistance of α-olefins in the chain-termination reaction of iron-initiated polymerization and regeneration of the active species for further polymerization. Besides higher activities of the catalytic system, the formation of linear PE with trans-vinylene terminal groups and lower molecular weights are explained. The observation will provide a new pathway for enhancing catalytic activity and improving the quality of polyethylenes obtained by regulation of molecular weights and molecular weight distribution.     

Application of a Recombinant Escherichia coli Whole‐Cell Catalyst Expressing Hydroxynitrile Lyase and Nitrilase Activities in Ionic Liquids for the Production of (S)‐Mandelic Acid and (S)‐Mandeloamide

The conversion of benzaldehyde and cyanide into mandelic acid and mandeloamide by a recombinant Escherichia coli strain which simultaneously expressed an (S)‐hydroxynitrile lyase (oxynitrilase) from cassava (Manihot esculenta) and an arylacetonitrilase from Pseudomonas fluorescens EBC191 was studied. Benzaldehyde exhibited a pronounced inhibitory effect on the nitrilase activity in concentrations ≥25 mM. Therefore, it was tested if two‐phase systems consisting of a buffered aqueous phase and the ionic liquid 1‐butyl‐1‐pyrrolidinium bis(trifluoromethanesulfonyl)imide (BMpl NTf₂) or 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMim PF₆) could be used for the intended biotransformation. The distribution coefficients of the substrates, intermediates and products of the reaction were determined and it was found that BMpl NTf₂ and BMim PF₆ were highly efficient as substrate reservoirs for benzaldehyde. The recombinant E. coli strain was active in the presence of BMpl NTf₂ or BMim PF₆ phases and converted benzaldehyde and cyanide into mandelic acid and mandeloamide. The two‐phase systems allowed the conversion of benzaldehyde dissolved in the ionic liquids to a concentration of 700 mM with product yields (=sum of mandelic acid and mandeloamide) of 87–100%. The cells were slightly more effective in the presence of BMpl NTf₂ than in the presence of BMim PF₆. In both two‐phase systems benzaldehyde and cyanide were converted into (S)‐mandeloamide and (S)‐mandelic acid with enantiomeric excesses ≥94%. The recombinant E. coli cells formed, in the two‐phase systems with ionic liquids and increased substrate concentrations, higher relative amounts of mandeloamide than in a purely aqueous system with lower substrate concentrations.