Banana MaBZR1/2 associate with MaMPK14 to modulate cell wall modifying genes during fruit ripening.

KEY MESSAGE: Banana MaBZR1/2 interact with MaMPK14 to enhance the transcriptional inhibition of cell wall modifying genes including MaEXP2, MaPL2 and MaXET5. Fruit ripening and softening, the major attributes to perishability in fleshy fruits, are modulated by various plant hormones and gene expression. Banana MaBZR1/2, the central transcription factors of brassinosteroid (BR) signaling, mediate fruit ripening through regulation of ethylene biosynthesis, but their possible roles in fruit softening as well as the underlying mechanisms remain to be determined. In this work, we found that MaBZR1/2 directly bound to and repressed the promoters of several cell wall modifying genes such as MaEXP2, MaPL2 and MaXET5, whose transcripts were elevated concomitant with fruit ripening. Moreover, yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays indicated that MaBZR1/2 physically interacted with a mitogen-activated protein kinase MaMPK14, and this interaction strengthened the MaBZR1/2-mediated transcriptional inhibitory abilities. Collectively, our study provides insight into the mechanism of MaBZR1/2 contributing to fruit ripening and softening, which may have potential for banana molecular improvement.

Thermal aggregation behaviour of soy protein: characteristics of different polypeptides and sub-units.

BACKGROUND: Due to the differences in structure and composition of glycinin and ß-conglycinin, they exhibit different characteristics during heat treatment. In present study, the thermal aggregation behaviour of glycinin, ß-conglycinin and their isolated sub-units was investigated at pH 7.0. RESULTS: Acidic polypeptides, basic polypeptides, αα' and ß sub-units of soy protein were denatured during the isolation process. The degree of aggregation of protein fractions after heat treatment was in the order: denatured basic polypeptides > native glycinin > denatured ß sub-unit > native ß-conglycinin > denatured acidic polypeptides > denatured αα' sub-units. Glycinin, ß-conglycinin, acidic polypeptides and αα'/ß sub-units exhibited different changing trends of surface hydrophobicity with increasing temperature. The αα' sub-units showed higher ability to suppress thermal aggregation of basic polypeptides than ß sub-units during heat treatment. The ß sub-units were shown to form soluble aggregates with glycinin after heating. CONCLUSION: The interaction mechanism of αα' and ß sub-units heated with basic polypeptides was proposed. For the ß sub-units-basic polypeptides mixed system, more hydrophobic chains were binding together and buried inside during heat treatment, which resulted in lower surface hydrophobicity. The αα' sub-units-basic polypeptides mixed system was considered to be a stable system with higher surface hydrophobicity after being heated.

Adsorption and dilatational rheology of heat-treated soy protein at the oil-water interface: relationship to structural properties.

We evaluated the influence of heat treatment on interfacial properties (adsorption at the oil-water interface and dilatational rheology of interfacial layers) of soy protein isolate. The related structural properties of protein affecting these interfacial behaviors, including protein unfolding and aggregation, surface hydrophobicity, and the state of sulfhydryl group, were also investigated. The structural and interfacial properties of soy protein depended strongly on heating temperature (90 and 120 °C). Heat treatment at 90 °C induced an increase in surface hydrophobicity due to partial unfolding of protein, accompanied by the formation of aggregates linked by disulfide bond, and lower surface pressure at long-term adsorption and similar dynamic interfacial rheology were observed as compared to native protein. Contrastingly, heat treatment at 120 °C led to a higher surface activity of the protein and rapid development of intermolecular interactions in the adsorbed layer, as evidenced by a faster increase of surface pressure and dilatational modulus. The interfacial behaviors of this heated protein may be mainly associated with more flexible conformation and high free sulfhydryl group, even if some exposed hydrophobic groups are involved in the formation of aggregates. These results would be useful to better understand the structure dependence of protein interfacial behaviors and to expand utilization of heat-treated protein in the formulation and production of emulsions.

Growth kinetics of amyloid-like fibrils derived from individual subunits of soy ß-conglycinin.

The amyloid-like fibrillation of soy ß-conglycinin subunits (α, α', and ß) upon heating (0-20 h) at 85 °C and pH 2.0 was characterized using dynamic light scattering, circular dichroism (CD), binding to amyloid dyes (Thioflavin T and Congo red), and atomic force microscopy. The fibrillation of all three subunits was accompanied by progressive polypeptide hydrolysis. The hydrolysis behaviors, fibrillation kinetics, and morphologies of amyloid-like fibrils considerably varied among α, α', and ß subunits. Faster hydrolysis rates and special fragments were observed for the α and α' subunits compared to the ß subunit. However, the order of the fibrillation rate and capacity to form ß-sheets was α' > ß > α, as evidenced by CD and Thioflavin T data. Moreover, sequential growth of twisted screw-structure fibrils, leading to macroscopic fibrils with distinct morphological characteristics, was observed for ß-conglycinin and individual subunits. The different fibrillation kinetics and morphologies of α, α', and ß subunits appear to be associated with the differences in the amino acid composition and typical sequence of peptides. Besides, the disruption of ordered structure of fibrils occurred upon further heating (6-20 h) due to extensive hydrolysis. These results would suggest that all subunits are involved in the fibrillation of ß-conglycinin, following multiple steps including polypeptide hydrolysis, assembly to amyloid structure, and growth into macroscopic fibrils with a fibril shaving process.

Structural rearrangement of ethanol-denatured soy proteins by high hydrostatic pressure treatment.

The effects of high hydrostatic pressure (HHP) treatment (100-500 MPa) on solubility and structural properties of ethanol (EtOH)-denatured soy ß-conglycinin and glycinin were investigated using differential scanning calorimetry, Fourier transform infrared and ultraviolet spectroscopy. HHP treatment above 200 MPa, especially at neutral and alkaline pH as well as low ionic strength, significantly improved the solubility of denatured soy proteins. Structural rearrangements of denatured ß-conglycinin subjected to high pressure were confirmed, as evidenced by the increase in enthalpy value (ΔH) and the formation of the ordered supramolecular structure with stronger intramolecular hydrogen bond. HHP treatment (200-400 MPa) caused an increase in surface hydrophobicity (F(max)) of ß-conglycinin, partially attributable to the exposure of the Tyr and Phe residues, whereas higher pressure (500 MPa) induced the decrease in F(max) due to hydrophobic rearrangements. The Trp residues in ß-conglycinin gradually transferred into a hydrophobic environment, which might further support the finding of structural rearrangements. In contrast, increasing pressure induced the progressive unfolding of denatured glycinin, accompanied by the movement of the Tyr and Phe residues to the molecular surface of protein. These results suggested that EtOH-denatured ß-conglycinin and glycinin were involved in different pathways of structural changes during HHP treatment.