Cell-Type-Specific Expression of Plant Cytochrome cmRNA in Developing Flowers and Roots

Abstract

We have used RNA in situ hybridization to analyze the expression of transcripts encoding cytochrome c in different tissues and organs of sunflower (Helianthus annuus). Although northern-blot hybridization experiments indicate that the relative abundance of transcripts does not vary greatly, we have detected important changes in localization during flower development. Enhanced expression is observed in floral meristems as soon as they are discernible from the central portion of the capitulum containing the inflorescence meristem. As flowers develop, labeling is observed in all developing floral organ primordia. Later in development, expression in petals is reduced, and only the central portion of the flower becomes labeled. During the process of stamen formation, hybridization signals were obtained mainly in anthers. Less developed flowers at this stage showed expression through the archesporial tissue. During meiosis, the label was observed mainly in tapetal cells. Specific expression patterns, similar to those obtained for sunflower, were observed when Arabidopsis flowers were analyzed with a homologous cytochrome c probe. Specific patterns of expression were also observed in young sunflower roots. In this case, enhanced expression was detected in developing endodermis and pericycle and in protoxylem initials. We conclude that cell-specific mechanisms operate to regulate the abundance of cytochrome c encoding transcripts in different plant tissues. The overlap between the expression patterns of the nuclear encoded cytochrome c gene and some mitochondrial genes suggests the existence of coordinated mechanisms of expression.

Differential Expression of the Arabidopsis Cytochrome c Genes Cytc-1 and Cytc-2. Evidence for the Involvement of TCP-Domain Protein-Binding Elements in Anther- and Meristem-Specific Expression of the Cytc-1 Gene

“…The expression patterns observed with the Cytc-1 promoter closely match the distribution of transcripts determined by in situ hybridization studies in both sunflower and Arabidopsis (Ribichich et al, 2001). In that study, transcripts were detected mainly in anthers and root meristems, but no specific hybridization was evident in mature leaves, although expression in these organs was observed in northern experiments (Felitti et al, 1997;Welchen et al, 2002).…”

“…This fits well with the fact that the number of mitochondria per cell increases considerably during flower development (Lee and Warmke, 1979). In situ hybridization studies have shown that the expression in flowers is cell-type specific and that there is a good correlation in the expression of several mitochondrial genes (Smart et al, 1994) and the nuclear gene encoding cytochrome c (Ribichich et al, 2001), suggesting the existence of coordinated regulatory mechanisms. Besides this organ-or cell-type-specific expression, we have observed that cytochrome c transcript levels are modified by incubation of plants in solutions containing metabolizable sugars or nitrogen salts (Felitti and Gonzalez, 1998;Welchen et al, 2002).…”

“…In that study, transcripts were detected mainly in anthers and root meristems, but no specific hybridization was evident in mature leaves, although expression in these organs was observed in northern experiments (Felitti et al, 1997;Welchen et al, 2002). One can speculate that the northern results with leaf RNA represent low-level expression in all leaf cell types, thus explaining the lack of signal in in situ hybridization (Ribichich et al, 2001) and GUS histochemical analysis (this study). However, this low-level expression was not even detected in GUS activity measurements using leaf protein extracts.…”

“…It has been shown that several nuclear genes encoding mitochondrial polypeptides are preferentially expressed in flowers (Huang et al, 1994;Felitti et al, 1997;Heiser et al, 1997). Studies using in situ hybridization and promoter/gus fusions have shown that localized expression in anthers seems to be a common feature of most genes encoding respiratory chain components (Zabaleta et al, 1998;Ribichich et al, 2001;Elorza et al, 2004;Welchen et al, 2004). Expression in other parts of the plant, however, is different depending on the particular gene analyzed.…”

Post-transcriptional Regulation in Mitochondria of Rice and Wheat at Low Temperatures

“…Reproductive organs have high mitochondrial biogenesis activity 17,24,43,61,71 . Accordingly, if mitochondrial abnormalities can be ameliorated, rice fertility will improve in cold weather years.…”