The ecdysteroid 20-hydroxyecdysone (20E) is a steroid hormone found in arthropods and plants. It is suspected to have agrochemical, biotechnological, medicinal, and pharmaceutical applicability. In insects, 20E controls or elicits molting and other developmental processes, and several characterized P450 enzymes are involved in its biosynthesis. In plants, it may act as a defensive substance against insects and nematodes. It is suspected that 20E, being a physiologically active compound, may affect morphological and physiological processes in plants and that C 27 phytosterols may be its precursors. However, neither its precise function nor its mechanism of biosynthesis in plants is fully understood. Here, the importance of 20E and current understanding of its structure, potential functions, and biosynthesis in both plants and insects are reviewed.Résumé : L'ecdysteroïde, le stéroïde hormonal 20-hydroxyecdysone (20E), se retrouve chez les arthropodes et les plantes. On croit qu'il aurait des applications agrochimiques, biotechnologiques, médicinales et pharmaceutiques. Chez les insectes, le 20E contrôle ou induit la mue et autres processus morphogénétiques, et on compte plusieurs enzymes P450 caractérisées impliquées dans sa biosynthèse. Chez les plantes, il peut agir comme substance de défense contre les insectes et les néma-todes. On croit que le 20E, une substance physiologiquement active, pourrait affecter des processus morphologiques et physiologiques chez les plantes et que des phytostérols en C27 pourraient en être les précurseurs. Cependant, on ne comprend pas complètement sa fonction précise ni le mécanisme de sa biosynthèse. Les auteurs passent en revue la compré-hension actuelle de sa structure, de ses fonctions potentielles et de sa biosynthèse, chez les plantes et chez les insectes.

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-This study aimed to characterize the genetic diversity of buriti populations by AFLP (Amplified Fragment Length

The sucrose binding protein (SBP) from soybean has been implicated as an important component of the sucrose uptake system. Two SBP genomic clones, gsS641.1 and gsS641.2, which correspond to allelic forms of the GmSBP2/S64 gene, have been isolated and characterized. As a member of the seed storage protein superfamily, it has been shown that the SBP gene structure is similar to vicilin genes with intron/exon boundaries at conserved positions. Fluores cence in situ hybridization (FISH) suggested that the soybean SBP gene family is represented by at least two non-allelic genes corresponding to the previously isolated GmSBP1 and GmSBP2/S64 cDNAs. These two cDNAs share extensive sequence similarity but are located at different loci in the soybean genome. To investigate transcriptional activation of the GmSBP2 gene, 2 kb 5'-flanking sequences of gsS641.1 and gsS641.2 were fused to the beta-glucuronidase (GUS) reporter gene and to the green fluorescent protein (GFP) reporter gene and inde pendently introduced into Nicotiana tabacum by Agrobacterium tumefaciens-mediated transformation. The SBP2 promoter directed expression of both GUS and GFP reporter genes with high specificity to the phloem of leaves, stems and roots. Thus, the overall pattern of SBP-GUS or SBP-GFP expression is consistent with the involvement of SBP in sucrose translocation-dependent physiological processes.

The Glycine max sucrose binding protein (GmSBP2) promoter directs phloem-specific expression of reporter genes in transgenic tobacco. Here, we identified cis-regulatory domains (CRD) that contribute with positive and negative regulation for the tissue-specific pattern of the GmSPB2 promoter. Negative regulatory elements in the distal CRD-A (-2000 to -700) sequences suppressed expression from the GmSBP2 promoter in tissues other than seed tissues and vascular tissues of vegetative organs. Deletion of this region relieved repression resulting in a constitutive promoter highly active in all tissues analyzed. Further deletions from the strong constitutive -700GmSBP2 promoter delimited several intercalating enhancer-like and repressing domains that function in a context-dependent manner. Histochemical examination revealed that the CRD-C (-445 to -367) harbors both negative and positive elements. This region abolished promoter expression in roots and in all tissues of stems except for the inner phloem. In contrast, it restores root meristem expression when fused to the -132pSBP2-GUS construct, which contains root meristem expression-repressing determinants mapped to the 44-bp CRD-G (-136 to -92). Thus, the GmSBP2 promoter is functionally organized into a proximal region with the combinatorial modular configuration of plant promoters and a distal domain, which restricts gene expression to the vascular tissues in vegetative organs.

The sucrose binding protein (SBP) has been implicated as an important component of the sucrose uptake system in plants. SBP-mediated sucrose transport displays unique kinetic features and the protein is not similar to other transport proteins. Here, we report the characterization of a member of the SBP family from soybean [Glycine max (L) Merrill] designated S64 or SBP2. Subcellular fractionation and precipitation by GTP-agarose demonstrated that S64/SBP2 is a membrane-associated protein that exhibits GTP binding activity. Purified recombinant S64/SBP2 protein, expressed as a histidine-tagged protein in Escherichia coli, exhibited nucleotide-binding specificity to guanine nucleotides. The GTP binding site was mapped to an imperfect Walker A type-sequence, Ala279-Leu-Ala-Pro-Thr-Lys-Lys-Ser286, by site-directed mutagenesis. Escherichia coli-produced wildtype protein and a truncated version of the protein containing the putative binding-sequence-bound GTP, although not with the same efficiency. In contrast, replacement of Thr283 and Lys284 residues to Leu and Glu residues prevented GTP binding. The site directed mutant failed to bind GTP but retained the ability to undergo oligomerization and to promote growth of the susy7 yeast strain, deficient in utilizing extracellular sucrose, on medium containing sucrose as the sole carbon source. Our results indicate that GTP binding and sucrose transport by SBP are separable and function independently. The implications of our findings with respect to the function and membrane topology of SBP are discussed.Keywords: sucrose transporter; soybean; yeast complementation assay; Glycine max.In many higher plants, sucrose is the predominant form of photoassimilate that is transported from mature leaves (source tissues) to sink tissues, such as seeds, stems, reproductive organs and roots, via the vascular system [1]. Biochemical studies have demonstrated that sucrose uptake kinetics in leaves is complex and consists of multiple components; for example, in Vicia faba, two saturable (high-and low-affinity) components and one linear, low-affinity component have been described [2]. Our understanding of sucrose translocation has advanced considerably over the last decade with the molecular and biochemical characterization of the sucrose transporter (SUT) family of low-and high-affinity sucrose transporters [1]. The SUT1 protein has been described as the protonmotive-force-driven sucrose symporter that mediates phloem loading and long-distance transport, the key transport step in assimilate partitioning for many plants [3][4][5]. SUT1 serves as a high-affinity transporter, whereas SUT4, a second member of this sucrose transporter family, corresponds to the low-affinity/high capacity saturable component of sucrose uptake found in leaves [6]. A third structurally related-member of the family has been identified and designated SUT2 [7]. The SUT2 protein has been proposed to act as a sugar sensor that controls sucrose fluxes across the plasma membrane of sieve elements by regulating express...

The ecdysteroid 20-hydroxyecdysone (20E) is a steroid hormone found in insects and few plants. To analyze its temporal and spatial distribution in Pfaffia glomerata (Amaranthaceae), we selected among 71 accessions, the accession 13 which showed the highest root 20E total quantity (1.48 g/plant root). The 20E was constantly detected in flowers, leaves, stems, and roots, but its percentage was variable throughout its development. The highest 20E percentage was found in flowers (0.82%), roots (0.66%), leaves (0.60%), and stems (0.24%). While stems showed the least variable 20E percentage (0.13% -0.24%), followed by roots (0.42% -0.66%), and flowers (0.47% -0.82%). Leaves showed the greatest 20E percentage variation (0.21% -0.60%). The stem and leaves 20E total amount remained constant, showing a little variation while root 20E total amount increased over time, suggesting that 20E may be accumulated in roots. These findings suggest that 20E has tissue specific functions in plant and may have ecological significance since uncoordinated pulses of 20E are often lethal to insects.