Ping Lang

Cold acclimation induced genes of trifoliate orange (Poncirus trifoliata)

Commercial citrus varieties are sensitive to low temperature. Poncirus trifoliata is a close relative of Citrus species and has been widely used as a cold-hardy rootstock for citrus production in low-temperature environments. mRNA differential display-reverse transcription (DDRT)-PCR and quantitative relative-RT-PCR were used to study gene expression of P. trifoliata under a gradual cold-acclimation temperature regime. Eight up-regulated cDNA fragments were isolated and sequenced. These fragments showed high similarities at the amino acid level to the following genes with known functions: betaine/proline transporter, water channel protein, aldo-keto reductase, early light-induced protein, nitrate transporter, tetratricopeptide-repeat protein, F-box protein, and ribosomal protein L15. These cold-acclimation up-regulated genes in P. trifoliata are also regulated by osmotic and photo-oxidative signals in other plants.

Sequence variation at cpDNA regions of watermelon and related wild species: implications for the evolution of Citrullus haplotypes

Sequencing analysis of one coding and four noncoding cpDNA regions was conducted to infer biogeographic and evolutionary relationships in the genus Citrullus. Eighteen taxa from diverse geographical areas were included. A low number of parsimony informative characters (1.1%) was observed at the ∼4 kb section of cpDNA. Variability within Citrullus was detected primarily at noncoding regions of high A + T content. Substitution rates varied from 0-0.48% for ndhF with A + T content of 68.4% to 0.39- 1.69% for the intergenic region of atpA with A + T content of 82.8%, mainly resulting in indels and transversions. Indels at several regions acted as valuable parsimony informative markers. Citrullus lanatus var. lanatus, the cultivated watermelon, and C. ecirrhosus and C. rehmii from Namibia, lacked molecular variability. The genus Citrullus is supported monophyletically and shows two main clades, one of which contains C. colocynthis. In the other clade, C. rehmii is sister to a clade containing C. ecirrhosus and C. lanatus. Two clades were recovered within C. lanatus, consisting of domesticated watermelon and wild citron, var. citroides. Five haplotypes within C. colocynthis were used to deduce colonization routes of the species. Biogeographic patterns point to separate colonization events into Africa and the Far East.

Phylogeny of Castanea (Fagaceae) based on chloroplast trnT-L-F sequence data

Species in the genus Castanea are widely distributed in the deciduous forests of the Northern Hemisphere from Asia to Europe and North America. They show floristic similarity but differences in chestnut blight resistance especially among eastern Asian and eastern North American species. Phylogenetic analyses were conducted in this study using sequences of three chloroplast noncoding trnT-L-F regions. The trnT-L region was found to be the most variable and informative region. The highest proportion of parsimony informative sites, more and larger indels, and higher pairwise distances between taxa were obtained at trnT-L than at the other two regions. The high A+T values (74.5%) in the Castanea trnT-L region may explain the high proportion of transversions found in this region where as comparatively lower A+T values were found in the trnL intron (68.35%) and trnL-F spacer (70.07%) with relatively balanced numbers of transitions and transversions. The genus Castanea is supported as a monophyletic clade, while the section Eucastanon is paraphyletic. C. crenata is the most basal clade and sister to the remainder of the genus. The three Chinese species of Castanea are supported as a single monophyletic clade, whose sister group contains the North American and European species. There is consistent but weak support for a sister–group relationship between the North American species and European species.

Down-regulated gene expression of cold acclimated Poncirus trifoliata

Citrus sp. are important commercial fruit crops throughout the world that are occasionally devastated by subfreezing temperatures. Poncirus trifoliata (maximum freeze tolerance of -26°C) is a close relative of commercial Citrus sp. (maximum freeze tolerance of -10°C) that has been used in breeding programs to develop more cold-hardy genotypes and as a rootstock to enhance freeze tolerance of the scion. Species with greater freeze tolerance vary in gene expression during cold acclimating temperatures. mRNA differential display (DDRT-PCR) and quantitative relative RT-PCR were used to study down regulation of gene expression in intact P. trifoliata exposed to a gradual cold acclimation regime to enhance our understanding of the mechanism that makes this specie so freeze tolerant. Six down-regulated genes were isolated and sequenced. These down-regulated genes showed high homology to the following known genes: chlorophyll a/b binding protein, photosystem II OEC 23, carbonic anhydrase, tumor related protein, p...