Two Different Endo-β-1,4-Glucanases Contribute to the Softening of the Strawberry Fruits

Purification and properties of an endo-β-1,4-glucanase from strawberry and down-regulation of the corresponding gene, cel1

“…Brighton and Elsanta, respectively. The molecular mass of our puri®ed Cel1 enzyme is in agreement with the value obtained by Trainotti et al(1999a) from a western blot of total soluble proteins but diers from that reported by Harpster et al (1998) estimated from a western blot of proteins extracted from acetone powders. Our puri®ed enzymeshowed maximum activity in the pH range 5.0±7.0 in accordance with the pH optima described for EGs isolated from other species (Brummell et al 1994).…”

“…Brighton has a high degree of similarity, but is not identical, to the corresponding cel1 homologues reported recently from cvs. Chandler and Selva (Harpster et al 1998;Llop-Tous et al 1999;Trainotti et al 1999a). The deduced amino acid sequences reveal subtle dierences in the EG proteins from these cultivars, in particular, the Ce11 from cv.…”

“…The reason for the preferential isolation of the Cel1 protein from strawberry by cellulose anity chromatography is unclear. The predicted pI of Cel2 from strawberry is 9.9 but an EG protein, presumed to be Cel2, that was separated by isoelectric focusing had a pI of 7.9 (Trainotti et al 1999a). One explanation could be that the Cel2 enzyme either does not bind to cellulose or, once bound, is not eluted under the conditions used.…”

“…The softening of strawberry fruit could be explained by EG acting on xyloglucan, possibly in concert with other cell-wallmodifying proteins such as expansins, disrupting the cellulose-xyloglucan network with the resultant loosening of the cell wall. Evidence for this comes from ultrastructural studies that show a progressive disorganization of cellulose micro®brils within the cell walls of white fruit (Trainotti et al 1999a). A reduction in the molecular size of the hemicellulose fraction from the fruit is evident before the white stage and it may be that Cel2 acts on xyloglucan prior to the ripening-related induction of Cel1.…”

“…The ®rst of these to be reported, cel1 (Manning 1998a), is encoded by a gene that is expressed speci®cally in ripening fruit. The detection of EG activity in unripe fruit (Harpster et al 1998) and the separation of two isoforms of EG with diering isoelectric points in ripe fruit (Trainotti et al 1999a) indicated another EG was expressed in this tissue. The second strawberry EG gene identi®ed (cel2) had a dierent spatial pattern of expression from cel1, its mRNA being detected in young vegetative tissues including leaves, stolons and young plantlets (Trainotti et al 1999b) as well as in young green fruit (Llop-Tous et al 1999;Trainotti et al 1999b).…”