Edited by Ulf-Ingo Flügge Keywords:Anthocyanin biosynthesis Arabidopsis HY5 PAP1 a b s t r a c t Several positive transcription factors regulate Arabidopsis anthocyanin biosynthesis. HY5, a component of light-signaling pathways, and PAP1, an R2R3-MYB transcription factor, share common regulatory targets on anthocyanin biosynthesis genes. The epistatic interactions between the two transcription factors are currently unknown. To address this problem, we analyzed crosses between hy5 and pap1 mutants (hy5pap1) or pap1D overexpressors (hy5pap1D), performed chromatin immunoprecipitation-qPCR, and determined the PAP1 promoter region through deletion analysis. The results show that HY5 regulates PAP1 expression via direct binding to G-and ACE-boxes in the promoter region, which suggests bifurcate regulation of anthocyanin biosynthesis by HY5 via transcriptional activation of PAP1.

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Biochemical evidence reported so far suggests that rubber synthesis takes place on the surface of rubber particles suspended in the latex of Hevea brasiliensis. We have isolated and characterized a cDNA clone that encodes a protein tightly bound on a small rubber particle. We named this protein small rubber particle protein (SRPP). Prior to this study, this protein was known as a latex allergen, and only its partial amino acid sequence was reported. Sequence analysis revealed that this protein is highly homologous to the rubber elongation factor and the Phaseolus vulgaris stress-related protein. Southern and Northern analyses indicate that the protein is encoded by a single gene and highly expressed in latex. An allergenicity test using the recombinant protein confirmed that the cloned cDNA encodes the known 24-kDa latex allergen. Neither ethylene stimulation nor wounding changed the transcript level of the SRPP gene in H. brasiliensis. An in vitro rubber assay showed that the protein plays a positive role in rubber biosynthesis. Therefore, it is likely that SRPP is a part of the rubber biosynthesis machinery, if not the rubber polymerase, along with the rubber elongation factor.Rubber (cis-1,4-polyisoprene), an isoprenoid polymer with no known physiological function to the plant, is produced in about 2000 plant species with varying degrees of quality and quantity (1). Rubber is the raw material of choice for heavy duty tires and other industrial uses requiring elasticity, flexibility, and resilience. Hevea brasiliensis has been the only commercial source of natural rubber mainly because of its abundance in the tree, its quality, and the ease of harvesting. The diminishing acreage of rubber plantations and life-threatening latex allergy to Hevea rubber, coupled with an increasing demand, have prompted research interests in the study of rubber biosynthesis and the development of alternative rubber sources.In H. brasiliensis, rubber synthesis takes place on the surface of rubber particles suspended in the latex (the cytoplasm of laticifers). The laticifers are specialized vessels that are located adjacent to the phloem of the rubber tree. When severed during tapping, the high turgor pressure inside the laticifers expels latex containing 30 -50% (w/w) cis-1,4-polyisoprene. The latex can be fractionated by centrifugation into three phases: the top fraction containing mostly rubber particles, the metabolically active middle fraction (called C-serum), and the bottom fraction of mainly vacuole-like organelles called lutoids. More than 240 expressed sequence tags (ESTs) 1 have been identified from the latex of H. brasiliensis 2 Kush et al. (2) have shown differential expression of several rubber biosynthesis-related genes in latex. The rubber elongation factor (REF), an enzyme involved in rubber biosynthesis (3), is highly expressed in laticifers (4). Laticiferous cells actively translate the transcribed genes into proteins. About 200 distinct polypeptides are present in the latex of H. brasiliensis (5). Arokiaraj et al...

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Summary• In higher plants, the plastidic glucose translocator (pGlcT) is assumed to play a role in the export of starch degradation products, but this has not yet been studied in detail.• To elucidate the role of pGlcT in the leaves of Arabidopsis thaliana, we generated single and double mutants lacking three plastidic sugar transporters, pGlcT, the triose-phosphate ⁄ phosphate translocator (TPT), and the maltose transporter (MEX1), and analyzed their growth phenotypes, photosynthetic properties and metabolite contents.• In contrast to the pglct-1 and pglct-2 single mutants lacking a visible growth phenotype, the double mutants pglct-1 ⁄ mex1 and tpt-2 ⁄ mex1 displayed markedly inhibited plant growth. Notably, pglct-1 ⁄ mex1 exhibited more severe growth retardation than that seen for the other mutants. In parallel, the most severe reductions in sucrose content and starch turnover were observed in the pglct-1 ⁄ mex1 mutant. The concurrent loss of pGlcT and MEX1 also resulted in severely reduced photosynthetic activities and extreme chloroplast abnormalities.• These findings suggest that pGlcT, together with MEX1, contributes significantly to the export of starch degradation products from chloroplasts in A. thaliana leaves, and that this starch-mediated pathway for photoassimilate export via pGlcT and MEX1 is essential for the growth and development of A. thaliana.