The R code of the proposed method is available at http://aspendb.uga.edu/downloads for academic use.

BackgroundBAHD acyltransferases are involved in the synthesis and elaboration of a wide variety of secondary metabolites. Previous research has shown that characterized proteins from this family fall broadly into five major clades and contain two conserved protein motifs. Here, we aimed to expand the understanding of BAHD acyltransferase diversity in plants through genome-wide analysis across five angiosperm taxa. We focus particularly on Populus, a woody perennial known to produce an abundance of secondary metabolites.ResultsPhylogenetic analysis of putative BAHD acyltransferase sequences from Arabidopsis, Medicago, Oryza, Populus, and Vitis, along with previously characterized proteins, supported a refined grouping of eight major clades for this family. Taxon-specific clustering of many BAHD family members appears pervasive in angiosperms. We identified two new multi-clade motifs and numerous clade-specific motifs, several of which have been implicated in BAHD function by previous structural and mutagenesis research. Gene duplication and expression data for Populus-dominated subclades revealed that several paralogous BAHD members in this genus might have already undergone functional divergence.ConclusionsDifferential, taxon-specific BAHD family expansion via gene duplication could be an evolutionary process contributing to metabolic diversity across plant taxa. Gene expression divergence among some Populus paralogues highlights possible distinctions between their biochemical and physiological functions. The newly discovered motifs, especially the clade-specific motifs, should facilitate future functional study of substrate and donor specificity among BAHD enzymes.

Although plants are envisioned to play a central role in life support systems for future long-duration space travel, plant growth in space has been problematic due to horticultural problems of nutrient delivery and gas resupply posed by the weightless environment. Iterative improvement in hardware designed for growth of plants on orbital platforms now provides confidence that plants can perform well in microgravity, enabling investigation of their nutritional characteristics. Plants of B. rapa (cv. Astroplants) were grown in the Biomass Production System on the International Space Station. Flowers were hand-pollinated and seeds were produced prior to harvest at 39 days after planting. The material was frozen or fixed while on orbit and subsequently analyzed in our laboratories. Gross measures of growth, leaf chlorophyll, starch and soluble carbohydrates confirmed comparable performance by the plants in spaceflight and ground control treatments. Analysis of glucosinolate production in the plant stems indicated that 3-butenylglucosinolate concentration was on average 75% greater in flight samples than in ground control samples. Similarly, the biochemical make-up of immature seeds produced during spaceflight and fixed or frozen while in orbit was significantly different from the ground controls. The immature seeds from the spaceflight treatment had higher concentrations of chlorophyll, starch, and soluble carbohydrates than the ground controls. Seed protein was significantly lower in the spaceflight material. Microscopy of immature seeds fixed in flight showed embryos to be at a range of developmental stages, while the ground control embryos had all reached the premature stage of development. Storage reserve deposition was more advanced in the ground control seeds. The spaceflight environment thus influences B. rapa metabolite production in ways that may affect flavor and nutritional quality of potential space produce.

Despite the importance of wild rice (Zizania palustris) in the Great Lakes region of North America, its sensitivity to sulfate is not well understood. A 21-d hydroponic experiment was performed to determine the toxicity of sulfate to wild rice seeds and seedlings. Effects of 6 sulfate concentrations ranging from 10 mg/L to 5000 mg/L and of chloride salts at equivalent conductivity were evaluated to determine whether adverse effects were attributable to sulfate or to conductivity-related stress. Sulfate treatment decreased root length, shoot length, and leaf number, and increased phytotoxic effects at concentrations of 5000 mg/L relative to a 50 mg/L control. The time to 30% mesocotyl emergence decreased at 2500 mg/L sulfate, indicating a potential stimulatory effect. Sulfate exposures of ≤ 5000 mg/L had no effect on 5 additional end points. Multiple regression analysis indicated that most observed changes could be attributed to conductivity-related stress rather than sulfate per se, with the exception of shoot length and leaf number. Chloride was more toxic than sulfate, as determined by root length and phytotoxicity. In summary, sulfate concentrations below 5000 mg/L did not adversely affect early-life stage wild rice during a 21-d period, and effects at 5000 mg/L sulfate were attributable to conductivity-related stress rather than sulfate toxicity in 2 of 4 end points.

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