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Tendrils are filamentous plant organs that coil on contact with an object, thereby providing mechanical support for climbing to reach more sunlight. Plant tendrils are considered to be modified structure of leaves, stems, or inflorescence, but the origin of cucurbit tendrils is still argued because of the complexity in the axillary organ patterning. We carried out morphological and genetic analyses of the Chiba Tendril-Less (ctl) melon (Cucumis melo) mutant, and found strong evidence that the melon tendril is a modified organ derived from a stem-leaf complex of a lateral shoot. Heterozygous (CTL/ctl) plants showed traits intermediate between tendril and shoot, and ontogenies of wild-type tendrils and mutant modified shoots coincided. We identified the CTL locus in a 200-kb region in melon linkage group IX. A single base deletion in a melon TCP transcription factor gene (CmTCP1) was detected in the mutant ctl sequence, and the expression of CmTCP1 was specifically high in wild-type tendrils. Phylogenetic analysis demonstrated the novelty of the CmTCP1 protein and the unique molecular evolution of its orthologs in the Cucurbitaceae. Our results move us closer to answering the long-standing question of which organ was modified to become the cucurbit tendril, and suggest a novel function of the TCP transcription factor in plant development.

Application of plant growth regulators may induce parthenocarpic fruit setting, avoiding problems due to poor pollination. Their influence on the ripening of netted-melon fruit (Cucumis melo L.), however, is not yet well understood. The ripening behavior of parthenocarpic melon fruit (treated with 50 ppm 4-chlorophenoxy acetic acid (p-CPA) and 350 ppm gibberellic acid (GA3) at anthesis) was compared with that of hand-pollinated fruit. The ethylene production in parthenocarpic fruit peaked up about 10 days behind that of pollinated fruit but was greater. The delay was accompanied by a retardation in fruit softening, thereby leading to an extended edible period. The expression of ethylene synthesis-related enzymes: ACC synthase (ACS) and ACC oxidase (ACO) genes at the commencement of the ripening process was also evaluated. Northern blot and RT-PCR analyses revealed a higher level in the mRNA transcript abundance of ACS genes (auxin- and wound-inducible) but lower abundance of the ripening-related gene ACO in parthenocarpic fruit compared to that of pollinated fruit. Western blot analysis further confirmed the lower level of ACO polypeptide in parthenocarpic fruit. The retarded ripening of parthenocarpic melon fruit resulted from the delayed production of ethylene, which is likely a consequence of the low abundance of ACO. A possible inhibitory effect of auxin on ACO transcript as a result of p-CPA application is proposed.

The 26S proteasome is known to play central roles in the growth of many eukaryotes. However, little is known regarding its distribution in higher plants. Here, we report the spatial distribution pattern of Rpn3 (a regulatory PA700 subunit) and C2 (a subunit of the 20S proteasome) in rice ( Oryza sativa L.) seedlings as determined by in situ hybridization. The transcripts were abundantly co-expressed in the apical and marginal meristems of shoots and roots. Interestingly, these transcripts also accumulated in the leaf and ligule primordia of the shoot apex. Our results suggest that the 26S proteasome is spatially distributed among various tissues and may be involved not only in cell division but also in organ formation in higher plants.

Three kinds of cDNAs encoding 26S proteasome subunits have been cloned from spinach (Spinacia oleracea L.). These genes, designated as SOPSC8, SOPSC1 and SOPRS7, encode an α-type and a β-type subunit of the 20S catalytic core, and an ATPase subunit of the 19/22S regulatory complex, respectively. The deduced protein sequences showed high sequence similarities to other proteasome α- and β-type and ATPase subunit proteins. Southern blot analysis indicates that there are additional members of these dispersed proteasome families in the spinach genome. These three subunit genes are expressed simultaneously during germination and reach a maximum one day after sowing followed by a decline. The expression of these genes also increases during cotyledon senescence.