Yuqiang Sun

The vascular cambium: molecular control of cellular structure.

Indeterminate growth and the production of new organs in plants require a constant supply of new cells. The majority of these cells are produced in mitotic regions called meristems. For primary or tip growth of the roots and shoots, the meristems are located in the apices. These apical meristems have been shown to function as developmentally regulated and environmentally responsive stem cell niches. The principle requirements to maintain a functioning meristem in a dynamic system are a balance of cell division and differentiation and the regulation of the planes of cell division and expansion. Woody plants also have secondary indeterminate mitotic regions towards the exterior of roots, stems and branches that produce the cells for continued growth in girth. The chief secondary meristem is the vascular cambium (VC). As its name implies, cells produced in the VC contribute to the growth in girth via the production of secondary vascular elements. Although we know a considerable amount about the cellular and molecular basis of the apical meristems, our knowledge of the cellular basis and molecular functioning of the VC has been rudimentary. This is now changing as a growing body of research shows that the primary and secondary meristems share some common fundamental regulatory mechanisms. In this review, we outline recent research that is leading to a better understanding of the molecular forces that shape the cellular structure and function of the VC.

Analysis of Flavonoids and the Flavonoid Structural Genes in Brown Fiber of Upland Cotton

Backgroud As a result of changing consumer preferences, cotton (Gossypium Hirsutum L.) from varieties with naturally colored fibers is becoming increasingly sought after in the textile industry. The molecular mechanisms leading to colored fiber development are still largely unknown, although it is expected that the color is derived from flavanoids. Experimental Design Firstly, four key genes of the flavonoid biosynthetic pathway in cotton (GhC4H, GhCHS, GhF3′H, and GhF3′5′H) were cloned and studied their expression profiles during the development of brown- and white cotton fibers by QRT-PCR. And then, the concentrations of four components of the flavonoid biosynthetic pathway, naringenin, quercetin, kaempferol and myricetin in brown- and white fibers were analyzed at different developmental stages by HPLC. Result The predicted proteins of the four flavonoid structural genes corresponding to these genes exhibit strong sequence similarity to their counterparts in various plant species. Transcript levels for all four genes were considerably higher in developing brown fibers than in white fibers from a near isogenic line (NIL). The contents of four flavonoids (naringenin, quercetin, kaempferol and myricetin) were significantly higher in brown than in white fibers and corresponding to the biosynthetic gene expression levels. Conclusions Flavonoid structural gene expression and flavonoid metabolism are important in the development of pigmentation in brown cotton fibers.

High codon adaptation in citrus tristeza virus to its citrus host

BackgroundCitrus tristeza virus (CTV), a member of the genus Closterovirus within the family Closteroviridae, is the causal agent of citrus tristeza disease. Previous studies revealed that the negative selection, RNA recombination and gene flow were the most important forces that drove CTV evolution. However, the CTV codon usage was not studied and thus its role in CTV evolution remains unknown.ResultsA detailed comparative analysis of CTV codon usage pattern was done in this study. Results of the study show that although in general CTV does not have a high degree of codon usage bias, the codon usage of CTV has a high level of resemblance to its host codon usage. In addition, our data indicate that the codon usage resemblance is only observed for the woody plant-infecting closteroviruses but not the closteroviruses infecting the herbaceous host plants, suggesting the existence of different virus-host interactions between the herbaceous plant-infecting and woody plant-infecting closteroviruses.ConclusionBased on the results, we suggest that in addition to RNA recombination, negative selection and gene flow, host plant codon usage selection can also affect CTV evolution.

Artificial TALE as a Convenient Protein Platform for Engineering Broad-Spectrum Resistance to Begomoviruses

Transcription activator–like effectors (TALEs) are a class of sequence-specific DNA-binding proteins that utilize a simple and predictable modality to recognize target DNA. This unique characteristic allows for the rapid assembly of artificial TALEs, with high DNA binding specificity, to any target DNA sequences for the creation of customizable sequence-specific nucleases used in genome engineering. Here, we report the use of an artificial TALE protein as a convenient platform for designing broad-spectrum resistance to begomoviruses, one of the most destructive plant virus groups, which cause tremendous losses worldwide. We showed that artificial TALEs, which were assembled based on conserved sequence motifs within begomovirus genomes, could confer partial resistance in transgenic Nicotiana benthamiana to all three begomoviruses tested. Furthermore, the resistance was maintained even in the presence of their betasatellite. These results shed new light on the development of broad-spectrum resistance against DNA viruses, such as begomoviruses.

Molecular analysis of proanthocyanidins related to pigmentation in brown cotton fibre (Gossypium hirsutum L.)

The structural characteristics and component differences of proanthocyanidins in brown and white cotton fibres were identified by nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) analyses. Proanthocyanidins in brown and white cotton fibres were found to contain mainly procyanidin (PC) and prodelphidin (PD) units with 2, 3-cis form (epigallocatechin and epicatechin). However, part of the proanthocyanidins in the white cotton fibres were modified by acylation and were constitutively different from the proanthocyanidins in brown cotton fibres. The relative amount of PD was similar to that of PC in white cotton fibres, while proanthocyanidins in brown cotton fibres consisted mainly of PD units with a relative ratio of 9:1. In brown cotton fibres, the proanthocyanidin monomeric composition was consistent with the expression profiles of proanthocyanidin synthase genes, suggesting that anthocyanidin reductase represented the major flow of the proanthocyanidin biosynthesis pathway. In addition, the structural characteristics and component differences of proanthocanidins in brown and white cotton fibres suggested that quinones, the oxidation products of proanthocyanidins, were the direct contributors to colour development in brown cotton fibre. This was demonstrated by vanillin-HCl staining and Borntragers test. Collectively, these data demonstrated that the biosynthesis of proanthocyanidins is a crucial pigmentation process in brown cotton fibre, and that quinones may represent the main pigments contributing to formation of the the brown colour. This study revealed the molecular basis of pigmentation in brown cotton fibres, and provided important insights for genetic manipulation of pigment production in cotton fibres.

Identification of the proteins in green cotton fiber using a proteomics-based approach.

The proteome of 21 DPA (days post-anthesis) of green cotton fiber was analyzed using two-dimensional gel electrophoresis to yield the first reference proteome map. Of 220 individual spots that were excised and analyzed by MALDI-TOF/TOF MS, 156 were identified and cataloged according to their functions. Twelve classes of proteins were identified. Many of these proteins were related to carbohydrate metabolism and energy production. Other notable functional classes included oxidoreductase, cell wall-related and cytoskeleton proteins. This study gives a snapshot of the proteome in 21 DPA green cotton fiber and advances our understanding of molecular mechanisms related to pigment biosynthesis in green cotton fiber.Graphical Abstract

Cell Suspension Culture-Mediated Incorporation of the Rice Bel Gene into Transgenic Cotton

Cotton plants engineered for resistance to the herbicides, glyphosate or glufosinate have made a considerable impact on the production of the crop worldwide. In this work, embryogenic cell cultures derived from Gossypium hirsutum L. cv Coker 312 hypocotyl callus were transformed via Agrobacterium tumefaciens with the rice cytochrome P450 gene, CYP81A6 (bel). In rice, bel has been shown to confer resistance to both bentazon and sulfanylurea herbicides. Transformed cells were selected on a liquid medium supplemented alternately or simultaneously with kanamycin (50mg/L) and bentazon (4.2 µmol). A total of 17 transgenic cotton lines were recovered, based on the initial resistance to bentazon and on PCR detection of the bel transgene. Bel integration into the cotton genome was confirmed by Southern blot and expression of the transgene was verified by RT-PCR. In greenhouse and experimental plot trials, herbicide (bentazon) tolerance of up to 1250mg/L was demonstrated in the transgenic plants. Transgenic lines with a single copy of the bel gene showed normal Mendelian inheritance of the characteristic. Importantly, resistance to bentazon was shown to be stably incorporated in the T1, T2 and T3 generations of self-fertilised descendents and in plants outcrossed to another upland cotton cultivar. Engineering resistance to bentazon in cotton through the heterologous expression of bel opens the possibility of incorporating this trait into elite cultivars, a strategy that would give growers a more flexible alternative to weed management in cotton crops.

Molecular integration of light responses in Arabidopsis

Growth habit and developmental phase transitions in plants are acutely responsive to the quantity and quality of incident light. Information about neighbouring plants is primarily perceived by changes in the light environment. Arabidopsis is able to distinguish these changes through the phytochrome (PHYA-E) red light receptors that perceive changes in the red to far red (R:FR) ratio, and the cryptochrome and phototropin blue light receptors. Phytochrome, in its biologically active far-red light-absorbing form (Pfr), mediates its effects by directly binding with the basic helix-loop-helix (bHLH) phytochrome-interacting factors (PIFs). High R:FR ratios initiate phytochrome (Pfr)-PIF binding and PIF protein degradation. Low R:FR ratios photo-convert Pfr into the inactive form Pr allowing the gene expression that leads to a range of adaptations, including the shade avoidance responses. PIF1 regulates the expression of a number of genes by directly binding to a G-box element in their promoter. T-DNA insertional mutagenesis of a number of these genes results in pleiotropic effects associated with an altered capacity to respond appropriately to environmental cues, including those signalling changes in soil water status and the ambient light environment. The data show evidence of a perturbation of light regulated response processes, including germination, the shade avoidance responses, stomatal conductance, flowering and the circadian clock perturbation in the PIF-regulated gene mutants. The pif1,3,4,5 quadruple and one of the PIF-regulated gene mutants fail to show shade avoidance responses in older plants grown under shade inducing conditions. This suggests that the encoded proteins mediate a parallel pathway in the induction of the SAS. The implications of our findings for an understanding of how plants appropriately respond to changes in their environment will be discussed. Figure 1