A meristem-related gene from tomato encodes a dUTPase: analysis of expression in vegetative and floral meristems.

Abstract

A meristem-specific gene coding for deoxyuridine triphosphatase (EC 3.6.1.23) (dUTPase) in tomato was isolated, and its developmental expression in vegetative and floral apices was monitored. An 18-kD polypeptide, P18, was isolated as a consequence of its accumulation in arrested floral meristems of anantha mutant plants. The corresponding cDNA isolated from an expression library exhibited a 40 to 60% similarity with the pseudoprotease sequences of poxviruses, genes that have been suggested to encode dUTPases. Enzymatic tests and conservation of peptide motifs common to bacterial and vira1 genes verified that the P18 cDNA clone indeed represents a eukaryotic dUTPase. lmmunogold localization and in situ hybridization experiments showed that polypeptides and transcripts of dUTPase are maintained at high levels in apical meristematic cells of vegetative and floral meristems. dUTPase gene activity is also high in the potentially meristematic cells of the provascular and vascular system. Its expression is lower in the immediate parenchymal derivatives of the apical meristematic cells, and this downregulation marks, perhaps, the transition from totipotency to the first differentiated state. INTRODUCTIONPrimary tissues of the plant shoot and root arise continuously from apical meristems. Apical meristems differentiate during embryogeny and are developmentally autonomous. They retain their meristematic activity throughout the life cycle while generating primary tissues and new meristematic centers that form lateral organs (Walbot, 1985;Goldberg, 1988;Sussex, 1989;Poethig, 1990). Unlike vegetative meristems, floral meristems are not embryonic in origin. Transmissible physiological signals in the vegetative apex initiate floral evocation, which results in transformation to a floral apex (Bernier, 1988). Floral meristems, moreover, are considered to be determinate because in most cases they form only inflorescences. Understanding meristems is, therefore, a prerequisite for the understanding of plant development (Sussex, 1989). An impressive body of descriptive and classical experimental studies on this subject is discussed comprehensively by Esau (1977), Cutter (1980), and Steeves and Sussex (1989).In an attempt to dissect the developmental processes in tomato meristems, we undertook the isolation of gene markers common to all plant meristems and others that are more specific to floral meristems. The repertoire of soluble and insoluble proteins of growing leaves and mature flowers was compared with that of anantha floral meristems. Floral meristems of anantha mutant plants are arrested at an early To whom correspondence should be addressed. preorganogenesis stage and then duplicated repeatedly (Helm, 1951;Paddock and Alexander, 1952), thus providing an excellent source of meristematic tissue (Lifschitz, 1988). Selected polypeptides that appeared more abundant in anantha meristems were purified, antibodies were prepared, and cDNA clones were isolated. The tomato deoxyuridine triphosphatase (dUTPase) gene reported here was ...

The tomato 66.3-kD polyphenoloxidase gene: molecular identification and developmental expression.

“…Analysis of protein profiles containing ~1500 bands from anantha meristems, expanding leaves, and normal mature flowers was conducted to identify flower-specific and meristem-related genes (Samach et al, 1991;Pri-Hadash et al, 1992). In this article, we report the isolation of a 58-to 60-kD protein (hereafter P2) found to be abundant among proteins in the 100,000g pellet from anantha floral meristems and normal flowers but hardly detected in mature leaves.…”

“…In the accompanying article, we describe the isolation and developmental expression of a meristem-related gene coding for the tomato dUTPase (Pri-Hadash et al, 1992). P2 and the dUTPase genes are expressed in a complementary manner in vegetative and floral meristematic domains, as well as in almost every organ in which both genes are expressed (Figures 6E to 6F and Figures 7D and 7E).…”

“…Here we compare lhe relevant sequences of the two P2 genes with tyrosinases from S. glaucescens (S.g) (Huber et al, 1985), N. crassa (N.c) (Lerch et al, 1982;Huber et al, 1985), and M. musculus (M.m) (Müller et al, 1988), and with hemocyanin from E. californicum (E.c) (Scharlau et al, 1983 In the ovary, P2 is most conspicuous in the integuments of ovules ( Figure 6D) and in the style, where the antigen is found in the ground tissue but not in the conducting tissue ( Figure 6E). The expression in the style is contrasted with that of dUTPase ( Figure 6F) to demonstrate the complementary manner in which the two genes are expressed (see Discussion and Pri-Hadash et al, 1992). For control, the localization of the light-harvesting protein of photosystem II in a crosssection of a mature flower ( Figure 6G) is presented.…”

Determination and Cell Interactions in Reproductive Meristems.

“…Although the cells of each layer are not limited in their developmental potential, they may be functionally distinct. Evidence for this can be found in the different orientation of cell divisions in different layers and in the expression patterns of some genes that appear to reflect the layered organization of the meristem (Pri-Hadash et al, 1992;Shaharetal., 1992;Fleming etal., 1993;Meeks-Wagner, 1993, this issue).…”

Vegetative Apical Meristems.

“…Various approaches have been used in attempts to isolate meristem-specific genes. These approaches include using homology to known probes from mammalian systems, to differential hybridization of cDNA clones, to the use of plants with apical meristem amplification such as cauliflower (Kosugi et al, 1991;Medford et al, 1991a;Pri-Hadash et al, 1992;Shahar et al, 1992). Table 1 presents a summary of genes expressed in shoot apices and apical meristems.…”