Binding-protein expression is subject to temporal, developmental and stress-induced regulation in terminally differentiated soybean organs

Abstract

Binding protein (BiP) is a widely distributed and highly conserved endoplasmic-reticulum luminal protein that has been implicated in cotranslational folding of nascent polypeptides, and in the recognition and disposal of misfolded polypeptides. Analysis of cDNA sequences and genomic blots indicates that soybeans (Glycine max L. Merr.) possess a small gene family encoding BiP. The deduced sequence of BiP is very similar to that of other plant BiPs. We have examined the expression of BiP in several different terminally differentiated soybean organs including leaves, pods and seed cotyledons. Expression of BiP mRNA increases during leaf expansion while levels of BiP protein decrease. Leaf BiP mRNA is subject to temporal control, exhibiting a large difference in expression in a few hours between dusk and night. The expression of BiP mRNA varies in direct correlation with accumulation of seed storage proteins. The hybridization suggests that maturing-seed BiP is likely to be a different isoform from vegetative BiPs. Levels of BiP protein in maturing seeds vary with BiP mRNA. High levels of BiP mRNA are detected after 3 d of seedling growth. Little change in either BiP mRNA or protein levels was detected in maturing soybean pods, although BiP-protein levels decrease in fully mature pods. Persistent wounding of leaves by whiteflies induces massive overexpression of BiP mRNA while only slightly increasing BiP-protein levels. In contrast single-event puncture wounding only slightly induces additional BiP expression above the temporal variations. These observations indicate that BiP is not constitutively expressed in terminally differentiated plant organs. Expression of BiP is highest during the developmental stages of leaves, pods and seeds when their constituent cells are producing seed or vegetative storage proteins, and appears to be subject to complex regulation, including developmental, temporal and wounding.

Estresse hídrico com diferentes osmóticos em sementes de feijão e expressão diferencial de proteínas durante a germinação

“…Entre estas respostas ao estresse, encontramos fatores de transcrição (ZHU, 2001), proteínas de diversas classes, como as BiP (Binding Protein) (KALINSKI et al, 1995), Peroxidases (SIEGEL, 1993), proteínas LEA (Late embryogenesis abundant protein) (VERDOY et al, 2004), proteínas ricas em prolina (PRPs) (VERDOY et al, 2004) e Proteínas de Choque Térmico (Heat Shock Protein -HSPs), as quais deveriam ser específicas ao estresse de calor, porém, também são sintetizadas na presença de estresse hídrico ou como resposta universal ao estresse (VIERLING, 1991), sendo encontradas desde em procariotos até em eucariotos.…”

Protein Quality Control Mechanisms and Protein Storage in the Endoplasmic Reticulum. A Conflict of Interests?

“…Because many secretory proteins are N-glycosylated and because glycosylation is often important for protein folding and solubility, tunicamycin is a potent and widely used inducer of UPR but, obviously, tunica- (Kalinski et al, 1995;Shimoni et al, 1995;Muench et al, 1997). In developing seeds, UPR induction could be due to displacement of BiP from the transmembrane ER effectors because of its action as a chaperone on the newly synthesized storage proteins.…”

Posttranslational Removal of the Carboxyl-terminal KDEL of the Cysteine Protease SH-EP Occurs Prior to Maturation of the Enzyme

“…The fraction was washed twice with the homogenization buffer and resuspended with 1.5 ml of the buffer. The dissolved solution was centrifuged at 200 ϫ g for 5 min, and the supernatant was layered on a continuous 0.6 -1.6 M sucrose gradient and centrifuged at 100,000 ϫ g for 17 h. After the run was completed, the gradient was fractionated into 0.9-ml fractions and each fraction was analyzed by SDS-PAGE immunoblotting with antiserum against SH-EP or maize BiP (52).…”