JOINTLESS suppresses sympodial identity in inflorescence meristems of tomato

Interaction study of MADS-domain proteins in tomato

MADS-domain proteins are important transcription factors involved in many biological processes of plants. Interactions between MADS-domain proteins are essential for their functions. In tomato (Solanum lycopersicum), the number of MIKC(c)-type MADS-domain proteins identified has totalled 36, but a large-scale interaction assay is lacking. In this study, 22 tomato MADS-domain proteins were selected from six functionally important subfamilies of the MADS-box gene family, to create the first large-scale tomato protein interaction network. Compared with Arabidopsis and petunia (Petunia hybrida), protein interaction patterns in tomato displayed both conservation and divergence. The majority of proteins that can be identified as putative orthologues exhibited conserved interaction patterns, and modifications were mostly found in genes underlining traits unique to tomato. JOINTLESS and RIN, characterized for their roles in abscission zone development and fruit ripening, respectively, showed enlarged interaction networks in comparison with their Arabidopsis and petunia counterparts. Novel interactions were also found for members of the expanded subfamilies, such as those represented by AP1/FUL and AP3/PI MADS-domain proteins. In search for higher order complexes, TM5 was found to be the preferred bridge among the five SEP-like proteins. Additionally, 16 proteins with the MADS-domain removed were used to assess the role of the MADS-domain in protein-protein interactions. The current work provides important knowledge for further functional and evolutionary study of the MADS-box genes in tomato.

Shoot architecture in the VitaceaeThis article is one of a selection of papers presented at the symposium on Vitis at the XVII International Botanical Congress held in Vienna, Austria, in 2005

This paper examines the question of how the unique shoot architectural pattern of the Vitaceae, typically with leaf-opposed tendrils or inflorescences in a three-node modular repetitive pattern, can be related to the traditional concepts of monopodial and sympodial shoot development. Based on complete comparative morphological developmental studies of 13 species in six genera, supplemented with observations of 21 other taxa, we have found five shoot architectural patterns in the family. The pattern of shoot architecture is consistent within a species, but there may be more than one pattern present within a genus. Species that lack tendrils, thus exhibiting pattern 1, show sympodial growth. Taxa exhibiting patterns 2, 3, and 4, with tendrils at two of three nodes and with progressively one, two, or three axillary buds within the three-node cycle, grow monopodially, and taxa that exhibit pattern 5, with both tendrils and axillary buds at every node, achieve the pattern via either monopodial or sympodial growth, depending on the species. Although rare in the Vitaceae, pattern 1 is the only one shared with the sister family Leeaceae. We conclude that this was the original shoot architectural pattern, and that the monopodial pattern present in most species today is derived, and unique to the Vitaceae.

Short vegetative phase-like MADS-box genes inhibit floral meristem identity in barley

Analysis of the functions of Short Vegetative Phase (SVP)-like MADS-box genes in barley (Hordeum vulgare) indicated a role in determining meristem identity. Three SVP-like genes are expressed in vegetative tissues of barley: Barley MADS1 (BM1), BM10, and Vegetative to Reproductive Transition gene 2. These genes are induced by cold but are repressed during floral development. Ectopic expression of BM1 inhibited spike development and caused floral reversion in barley, with florets at the base of the spike replaced by tillers. Head emergence was delayed in plants that ectopically express BM1, primarily by delayed development after the floral transition, but expression levels of the barley VRN1 gene (HvVRN1) were not affected. Ectopic expression of BM10 inhibited spike development and caused partial floral reversion, where florets at the base of the spike were replaced by inflorescence-like structures, but did not affect heading date. Floral reversion occurred more frequently when BM1 and BM10 ectopic expression lines were grown in short-day conditions. BM1 and BM10 also inhibited floral development and caused floral reversion when expressed in Arabidopsis (Arabidopsis thaliana). We conclude that SVP-like genes function to suppress floral meristem identity in winter cereals.

Inflorescence development in two tomato species

The inflorescence of tomato has been characterized as either a cyme or raceme. Cymose inflorescences are determinate, whereas racemose inflorescences are indeterminate. In this study, we addressed the discrepancy in inflorescence architecture by analyzing the morphology of a wild relative of tomato Solanum pimpinellifolium L. and four domesticated Solanum lycopersicum L. lines. Careful observation of developing inflorescences of both species showed a bifurcation of the meristem into a determinate floral and an indeterminate inflorescence meristem. Interestingly, higher fruit carpel number was associated with delayed floral development, which might give the impression of determinate growth in some of the lines. Nevertheless, our results demonstrated that tomato inflorescences are indeterminate in nature regardless of the line studied. Floral buds were formed concomitantly with the development of the inflorescence meristem and not on the flanks of the peduncle, a characteristic of racemose growth. Thus, tomato inflorescences should be classified as a cyme with the note that the inflorescence meristem does not terminate into a flower and, in fact, maintains indeterminacy. In addition, S. pimpinellifolium produced many more flowers in a highly regular manner when compared with the cultivated types. This demonstrated the usefulness of wild relatives of tomato as a tool to further understand flower and fruit development in this crop species.