Immunolocalization of LeAGP-1, a modular arabinogalactan-protein, reveals its developmentally regulated expression in tomato

Abstract

Arabinogalactan-proteins (AGPs) are highly glycosylated cell surface proteins that are thought to function in plant growth and development. The developmentally regulated expression of LeAGP-1, a novel and major AGP in tomato, was examined in different organs and tissues of tomato (Lycopersicon esculentum Mill. cv. UC82B) plants with an anti-peptide antibody (i.e. the PAP antibody) directed specifically against the lysine-rich subdomain of the LeAGP-1 core protein. During cell differentiation in tomato plants, LeAGP-1 was associated with cell wall thickening and lignification of particular cell types. Specifically, LeAGP-1 was detected in secondary wall thickenings of maturing metaxylem and secondary xylem tracheary elements in roots and stems, and in thickened cell walls of phloem sieve elements. However, LeAGP-1 was also present in thin-walled, cortical parenchyma cells of seedling roots as well as thick-walled collenchyma cells in young stems, both of which are not lignified. Based on these observed patterns, possible roles for LeAGP-1 in plant growth and development are discussed.

Characterization of Synthetic Hydroxyproline-Rich Proteoglycans with Arabinogalactan Protein and Extensin Motifs in Arabidopsis

“…In most cases, the proteins were localized in epidermal cells [(SPPPP) 15 ]. The tissue expression of LeAGP1 in Arabidopsis stems is similar to that described for tomato stems (Gao et al, 1999;Gao and Showalter, 2000), although the epidermal cells were not reactive in the latter with the polyclonal PAP antibody (reacts against the Lys-rich subdomain of the Le-AGP1 protein backbone).…”

“…3A and 4, B and C). Similar tissue expression was found in tomato plants (Gao and Showalter, 2000). LeAGP1 orthologs in Arabidopsis (AtAGP17, AtAGP18, and AtAGP19) are Incubation of a leaf extract at room temperature (RT) with or without urea, before electrophoresis produced a band of expected molecular mass of the nonglycosylated construct (white arrowhead) together with other bands of higher M r , but no band is detected at 27 kD (*).…”

“…Thus, the AG in Arabidopsis are much larger than in BY2 cells. LeAGP1 expressed in Arabidopsis plants seems to have less dispersion and higher molecular mass compared with the smear of 37 to 105 kD found in the vegetative organs of tomato (Gao and Showalter, 2000), but the same molecular mass range when expressed in tobacco cells (Sun et al, 2004). LeAGP1 was present in all Arabidopsis tissues analyzed not only by western blots, but also by confocal laser-scanning microscopy (CLSM; Figs.…”

Arabinogalactan-proteins: structure, expression and function

“…For example, in tomato, LeAGP-1 messenger RNA (mRNA) is found in young but not old stems and fruit [12,13]. Interestingly, the LeAGP-1 glycoprotein is detected at both temporal stages, providing some support to the notion that AGPs are stable molecules once produced and may accumulate over time [75]. At the tissue (and cellular) level, immunolocalization studies have revealed developmental patterns of AGP expression.…”

“…(see table 2). More specifically, such AGPs are associated with, and hypothesized to function in, secondary cell wall thickening and programmed cell death (PCD) [39,75]. Here, AGPs which are located at the cell surface of differentiating xylem elements may serve to position or interact with wall components, including themselves, and thus contribute to wall thickening.…”