A diversity of mRNAs containing only short open reading frames (sORF-RNAs; encoding less than 30 amino acids) have been shown to be induced in growth and differentiation processes. The early nodulin gene enod40, coding for a 0.7-kb sORF-RNA, is expressed in the nodule primordium developing in the root cortex of leguminous plants after infection by symbiotic bacteria. Ballistic microtargeting of this gene into Medicago roots induced division of cortical cells. Translation of two sORFs (I and II, 13 and 27 amino acids, respectively) present in the conserved 5 and 3 regions of enod40 was required for this biological activity. These sORFs may be translated in roots via a reinitiation mechanism. In vitro translation products starting from the ATG of sORF I were detectable by mutating enod40 to yield peptides larger than 38 amino acids. Deletion of a Medicago truncatula enod40 region between the sORFs, spanning a predicted RNA structure, did not affect their translation but resulted in significantly decreased biological activity. Our data reveal a complex regulation of enod40 action, pointing to a role of sORF-encoded peptides and structured RNA signals in developmental processes involving sORF-RNAs.RNAs encoding only short open reading frames (sORFRNAs) have received considerable attention in recent years because they show a striking diversity in many cell types from various organisms. Several RNAs exhibit a function without being translated into proteins, for example, tRNAs, rRNAs, RNAs in ribozymes, and small nuclear RNAs from spliceosomes (reviewed in reference 8). However, a pentapeptideencoding sORF present in the 23S rRNA from Escherichia coli was recently shown to render this bacterium resistant to a specific antibiotic (40). In eukaryotes, several sORF-RNAs are induced at specific stages of development, suggesting their participation in various differentiation processes (7,14,18,31,38,40,44,46). Eukaryotic cells may use sORF-RNAs for the regulation of several cellular processes, as suggested by a thorough analysis of the yeast genome leading to identification of several new noncoding and sORF-containing RNAs (31). In eukaryotes, sORFs present in mRNAs are likely to be translated, since translation of mRNAs is achieved by a scanning mechanism in a 5Ј-to-3Ј direction. Indeed, there are several examples where translation of upstream sORFs regulates expression of the 3Ј ORF corresponding to the gene product (15,43). At the same time, very little is known about the fate of the encoded oligopeptides in the cell and whether translation of sORFs present in sORF-RNAs is relevant for gene activity. For example, even though a putative protein product of the H19 RNA was detected using immunological approaches (23), the main function of H19 seems to lie in the mRNA molecule rather than in the encoded protein (24).Leguminous plants have the ability to enter into symbiosis with N 2 -fixing bacteria (collectively called rhizobia) to form the root nodule. Development of this symbiotic organ depends on the coordinate expressio...

Under nitrogen-limiting conditions Rhizobium meliloti can establish symbiosis with Medicago plants to form nitrogen-fixing root nodules. Nodule organogenesis starts with the dedifferentiation and division of root cortical cells. In these cells the early nodulin gene enod40, which encodes an unusually small peptide (12 or 13 amino acids), is induced from the beginning of this process. Herein we show that enod40 expression evokes root nodule initiation.

Summary A serological assay for the quantitative determination of the novel tumour-associated epitope CA242 was developed and used for determination of sensitivity and specificity of CA242 in gastrointestinal cancer. The CA242 assay showed a better tumour specificity than CA50

The symbiosis between Gunnera and Nostoc was reconstituted using G. chilensis Lam. and G. manicata Linden, respectively, and three different Nostoc strains. Six stages characterised by specific modifications in both the cyanobiont and the host were recognised during the infection process. Mucilage-secreting stem glands developed on the Gunnera stems independent of the presence of cyanobacteria (Stage I). Soon after addition of the Nostoc isolates to the plant apices, an abundant differentiation of motile hormogonia commenced. The cyanobacteria accumulated in the mucilage on the surface of the gland (Stage II), and the hormogonia then proceeded into the stem tissue through intercellular channels (Stage III). At the channel bases, Nostoc was detected between the cell walls of small, densely cytoplasmic Gunnera cells and also in elaborate folds of these (Stage IV). The Gunnera cell walls subsequently dissolved adjacent to the cyanobacteria and Nostoc entered the host cells (Stage V). Once the intracellular association was formed, a high proportion of the vegetative Nostoc cells differentiated into heterocysts (Stage VI). Nostoc changed from being rich in inclusions (particularly cyanophycin) while on the gland surface into a comparatively "non-storing" form during penetration and the early intracellular stages. Bacteria were numerous on the gland surface, fewer in the channels, and were never detected within the Gunnera cells, indicating the existence of specific recognition mechanisms discriminating between conceivable microsymbionts. Mechanisms behind mutual adaptations and interactions between the two symbionts are discussed.