Accumulation of cell wall hydroxyproline-rich glycoprotein mRNA is an early event in maize embryo cell differentiation.

Abstract

The accumulation of the mRNA coding for a hydroxyproline-rich glycoprotein (HRGP), an abundant component of the wall from the cells of vegetative tissues, has been observed in maize embryo by in situ hybridization. The HRGP mRNA accumulates in the embryo axis and not in the scutellum and preferentially in dividing and provascular cells. The histone H4 mRNA is distributed in similar tissues but is restricted to defined groups of cells, indicating that these two gene products have a different steady-state level of accumulation during the cell cycle. The HRGP mRNA appears to be a useful marker for early formation ofthe vascular systems. The mRNA accumulation correlates in space and time with cells having a low content of cellulose in their walls, suggesting that the mRNA is produced in the early stages of cell wall formation before complete deposition of cellulose.Formation of the cell wall is an essential morphogenic event in plant cells. Different polysaccharide and protein components have been identified in the cell wall but the timing of deposition and assembly of these components is not known (1). The cell wall plays an important role in plant cell differentiation: some of its components, such as oligosaccharides, may induce specific developmental stages in tobacco thin layers (2) and a group of glycoproteins has been shown to complement mutations affecting defined steps during carrot somatic embryogenesis (3). Among the cell wall proteins, hydroxyproline-rich glycoproteins (HRGPs) are probably the best characterized. The extensins, HRGP components from dicotyledonous systems (4), have been characterized at the protein, cDNA, and genomic levels. In monocotyledonous species an analogous protein rich in threonine has been identified at the protein (5-7), cDNA (8), and genomic (9) levels in maize. Maize HRGP is a highly repetitive proline-and threonine-rich protein. Antibodies raised against the purified protein react with defined polypeptides in cell wall extracts, which have been localized in the cell wall by immunocytochemistry and immunoelectron microscopy (10,11). Previous results indicate that the Hrgp gene is active in response to different situations during cell life. The expression of the Hrgp gene parallels histone mRNA accumulation in tissues rich in dividing cells. HRGP mRNA is also found in wounded young organs (10). The mRNA coding for the maize HRGP is transiently accumulated at new vascular sites in germinating embryos, leaves, and roots (9).Tissue specificity has also been observed by immunological and Northern blot analyses in the maize embryo (11). In particular, the absence of both HRGP mRNA and protein in the scutellum has been observed. In accordance with these data, we have used a fragment of the coding region of the HRGP genomic clone as a probe to study the steps leading to formation of the cell wall in specific cell types during embryo development. We have analyzed the in situ hybridization patterns of HRGP mRNA accumulation in different stages of maize embryogenesis. The results...

Rapid changes induced in developmental programmes of the maize embryo detected by analysis of the expression of genes encoding proline‐rich proteins

“…After germi- nation and callogenesis induction, zmHRGP mRNA is induced in the scutellum, with a di¡erent cell expression pattern in each case. After germination the pattern of expression observed in the axis, as well as in the scutellum, is very similar to that described for H4, a marker of cell division actively expressed during embryo morphogenesis [6,7]. As zmHRGP and H4 have a similar time expression in hydrating immature maize embryos, we conclude that zmHRGP morphological expression pattern is associated with the new cell division centers activated by germination.…”

“…zmHRGP codes for a cell wall protein accumulated in tissues rich in dividing cells [5]. During embryo development zmHRGP expression is restricted to the morphogenetic stage and is absent from the scutellum [6,7] being a marker of suspensor and vascular tissue development [2,3]. In the present paper zmHyPRP and zmHRGP have been used as probes to study the changes occurring when development is altered by placing the immature embryos in di¡erent media [8,9].…”

Regulation of the maize HRGP gene expression by ethylene and wounding. mRNA accumulation and qualitative expression analysis of the promoter by microprojectile bombardment

“…The signals of the other samples were scaled according to these two reference values. In situ hybridization was performed as described [13,23].…”

“…In maize, a hydroxyproline-rich glycoprotein (HRGP) rich in threonine has been purified [ 11 ] corresponding to a cDNA clone and a gene already identified [25,26]. The modalities of expression of this maize HR GP gene have been characterized both at the m R N A and protein levels [16,22,23,26]. The spatial and temporal pattern of m R N A accumulation can be summarized as follows: (i) accumulation in dividing cells, (ii)transient overexpression in the vascular system and (iii)induction by wounding in young tissues.…”

Developmental and Hormonal Regulation of Genes Coding for Proline-Rich Proteins in Female Inflorescences and Kernels of Maize1

“…In contrast, the accumulation of HRGP mRNA shows a pattern complementary to that observed for HyPRP in the sense that in the immature embryo one gene is expressed in tissues in which the other is not expressed. In particular, HRGP mRNA is found abundantly in axis provascular cells, where HyPRP is not found (Josè-Estanyol et al, 1992;Ruiz-Avila et al, 1992). The mRNA of HyPRP disappears when ABA accumulation begins in the developing embryo with the initiation of the maturation and dessication phases (Jones and Brenner, 1987).…”