Tropical Plant Biology

Mazzafera, Paulo; Baumann, Thomas; Shimizu, Milton; Silvarolla, Maria

2009 Tropical Plant Biology

doi: 10.1007/s12042-009-9032-7

Unquestionably, the popularity of the coffee beverage relies on its alerting attribute caffeine. However, susceptibilities to this purine alkaloid, quite frequently associated with health concerns, encouraged a significant market for decaffeinated coffee. The beans of Coffea arabica render the best beverage and a decaffeinated coffee has to preserve the desired organoleptic characteristics of this species. Consequently, besides technical removal of caffeine, the endeavors to attain a decaffeinated Arabica coffee range from traditional studies on genetic variability to advanced techniques to produce genetic modified coffee. The aim of this review is to recover part of this subject focusing mainly on the natural genetic variation for caffeine content in Arabica. We also present historical information about caffeine discovery and briefly discuss molecular approaches to reduce caffeine. We introduce here the term decaffito for coffee derived from Arabica plants with beans naturally low in or almost devoid of caffeine. In the near future, coffee drinkers avoiding caffeine will have the choice between basically three Arabica coffees, namely decaffeinated by (a) selection and breeding, (b) genetic modification and (c) industrial extraction. Although only the last decaf coffee is available for the consumers, we believe that the size of the market of each type will occupy in the future depend on the price and health aspects related to the way the decaffeinated coffee beans are obtained.

Kapralov, Maxim; Stift, Marc; Filatov, Dmitry

2009 Tropical Plant Biology

doi: 10.1007/s12042-009-9029-2

Genome sizes may vary by orders of magnitude among relatively closely related species. Gene and genome duplications and movements of transposable elements (TEs) can quickly inflate genome sizes. Whole genome duplications (polyploidization) may be an important source of evolutionary innovation and many fast evolving island genera are known or assumed to be polyploids. Our main aim is to shed light on the question of how genome size evolved within a rapidly diversifying island lineage. We report the estimates of DNA content for 27 species of the Hawaiian endemic plant genus Schiedea and its widespread sister genus Honckenya (Caryophyllaceae: Alsinoideae). Unexpectedly, genomes of Schiedea species appeared to be relatively compact (1.41 to 3.74 pg/cell), compared to Honckenya (8.57 to 10.66 pg/cell). Interestingly, Schiedea species from younger islands tended to have larger genomes than species from older islands, which may be explained by activation of TE transpositions in small populations after colonization events that resulted in the formation of new species on younger islands. To test whether the Schiedea genome has undergone recent polyploidization events we measured divergence between 62 pairs of paralogous genes in S. globosa. The distribution of divergence values was unimodal with a mode of 7%, supporting a single polyploidization event. Dating this event using Schiedea/Honckenya divergence (2%) and Schiedea/Silene divergence (11%) we estimate that it might have occurred in the ancestor of the genera Schiedea and Honckenya, but after the split between the subfamilies Alsinoideae and Silenoideae.

Porter, Brad; Zhu, Yun; Christopher, David

2009 Tropical Plant Biology

doi: 10.1007/s12042-009-9030-9

Plant pathogenic Phytophthora species are predicted to encode a large arsenal of ‘effector’ proteins that target and disrupt normal host cell function, but genes regulated by effectors are difficult to distinguish from those more generally regulated by microbe associated molecular patterns (MAMPs). To help make this distinction, expression studies of host-Phytophthora interactions can be compared to reveal patterns of gene regulation indicative of effector activity. The recently sequenced tropical fruit tree, Carica papaya, contains fewer genes than Arabidopsis and is highly susceptible to the broad-host-range pathogen P. palmivora, offering a new system for comparative genomics. In this study, genes isolated from the transcriptome of C. papaya seedling roots inoculated with P. palmivora, were evaluated for pathogen-regulation. Of these genes, a predicted peroxidase, ß-1,3-glucanase, ferulate 5-hydroxylase, and hypersensitive-induced response protein were pathogen upregulated, while a second peroxidase (Cp9) and aquaporin (Cp15), both with normally high root expression, were down-regulated. Genes from other plants with similar expression responses to Phytophthora were identified from previously reported studies and evaluated for protein sequence similarity. Interestingly, as for papaya, Phytophthora also down-regulates homologs of Cp9 and Cp15 in Glycine max and Solanum tuberosum, respectively. Because peroxidases associated with defense are generally upregulated during infection and the regulation of aquaporins have been cited in cases of both plant (Opperman et al. Science 263:221–223, 1994) and animal disease (Guttman et al. Cell Microbiol 9:131–141, 2007), Cp9 and Cp15 are potential cross-species effector targets. With whole-genome C. papaya microarrays forthcoming, this study highlights papaya as a resource for comparative genomic studies of Phytophthora-plant interaction.

Felix, Juliana; Papini-Terzi, Flávia; Rocha, Flávia; Vêncio, Ricardo; Vicentini, Renato; Nishiyama, Milton; César Ulian, Eugênio; Souza, Gláucia; Menossi, Marcelo

2009 Tropical Plant Biology

doi: 10.1007/s12042-009-9031-8

Sucrose is the major product of photosynthesis in many higher plants. It is transported from the source tissue through the phloem to various sink tissues to support plant growth, development and reproduction. Knowledge on the signal transduction pathways involved in sucrose synthesis in mature leaves is limited. Using a microarray approach, we analyzed the expression profiles of 1920 sugarcane genes encoding signal transduction elements, transcription factors and stress-related proteins. We used individuals from a population segregating for sugar content and gene expression profiles were obtained from seven individuals with highest and seven with lowest sugar content. Surprisingly, from the 24 differentially expressed genes, 19 were more expressed in plants containing low-sugar content. Three of these genes encoded 14-3-3 like proteins, which have been found to reduce sucrose phosphate synthase (SPS) activity. Another encoded an SNF1-related protein similar to a protein kinase that phosphorylates SPS in vitro making it a target for the interaction with 14-3-3 proteins. The up-regulation of eight stress related genes in the lower sugar content plants supports a view that sugar levels modulate a complex signal transduction network that seems to involve responses that are related to stress. Evidence that hormone signaling is related to the sucrose content was also found. These data reinforced the usefulness of genomic approaches to uncover how sucrose metabolism can be regulated in sugarcane.