N-Acetylglucosamine and Glucosamine-Containing Arabinogalactan Proteins Control Somatic Embryogenesis

Abstract

In plants, complete embryos can develop not only from the zygote, but also from somatic cells in tissue culture. How somatic cells undergo the change in fate to become embryogenic is largely unknown. Proteins, secreted into the culture medium such as endochitinases and arabinogalactan proteins (AGPs) are required for somatic embryogenesis. Here we show that carrot (Daucus carota) AGPs can contain glucosamine and N-acetyl-d-glucosaminyl and are sensitive to endochitinase cleavage. To determine the relevance of this observation for embryogenesis, an assay was developed based on the enzymatic removal of the cell wall from cultured cells. The resulting protoplasts had a reduced capacity for somatic embryogenesis, which could be partially restored by adding endochitinases to the protoplasts. AGPs from culture medium or from immature seeds could fully restore or even increase embryogenesis. AGPs pretreated with chitinases were more active than untreated molecules and required an intact carbohydrate constituent for activity. AGPs were only capable of promoting embryogenesis from protoplasts in a short period preceding cell wall reformation. Apart from the increase in embryogenesis, AGPs can reinitiate cell division in a subpopulation of otherwise non-dividing protoplasts. These results show that chitinase-modified AGPs are extracellular matrix molecules able to control or maintain plant cell fate.

Proteins involved in biotic and abiotic stress responses as the most significant biomarkers in the ripening of Pinot Noir skins

“…Alternatively, it is also possible that they may have some role during berry ripening. For example, it was observed that some chitinases do not show any antifungal property in vitro (Kasprzewska 2003) while there is strong evidence that chitinases catalyze the hydrolytic decomposition of arabinogalactan proteins (AGPs) that are present in plant cell walls (van Hengel et al 2001(van Hengel et al , 2002.…”

The plant stigma exudate

“…In that respect, it is interesting to note that extracellular chitinases are able to use N-acetylglucosamine and glucosaminecontaining AGPs as substrates. 13 Alternatively, in partnership with other secreted proteins identified in the stigma exudate (e.g., S1-type nucleases), chitinases may take part in the PCD of the stigma after either compatible pollination or incompatible pollen rejection. 14 Temperature stress also affects several aspects of plant reproduction such as stigmatic receptivity, pollen performance and self-incompatibility relationships.…”

Genome-wide identification, expression and chromosomal location of the genes encoding chitinolytic enzymes in Zea mays

“…An endogenous substrate for plant chitinases has not yet been deWnitively identiWed. However, there is strong evidence that these enzymes catalyze the hydrolytic decomposition of arabinogalactan proteins (AGPs) present in plants (van Hengel et al 2001(van Hengel et al , 2002. Other N-acetylglucosamine-containing glycoproteins present in the cell wall may be endogenous substrates for plant chitinases (Berger et al 1995;Schultze et al 1998;van der Holst et al 2001;Dyachok et al 2002).…”