Identification and functional analysis of anthocyanin biosynthesis genes in <Emphasis Type="Italic">Phalaenopsis</Emphasis> hybrids

Phalaenopsis species are among the most popular potted flowers for their fascinating flowers. When their whole-genome sequencing was completed, they have become useful for studying the molecular mechanism of anthocyanin biosynthesis. Here, we identified 49 candidate anthocyanin synthetic genes in the Phalaenopsis genome. Our results showed that duplication events might contribute to the expansion of some gene families, such as the genes encoding chalcone synthase (PeCHS), flavonoid 3′-hydroxylase (PeF3′H), and myeloblastosis (PeMYB). To elucidate their functions in anthocyanin biosynthesis, we conducted a global expression analysis. We found that anthocyanin synthesis occurred during the very early flower development stage and that the flavanone 3-hydroxylase (F3H), F3′H, and dihydroflavonol 4-reductase (DFR) genes played key roles in this process. Over-expression of Phalaenopsis flavonoid 3′,5′-hydroxylase (F3′5′H) in petunia showed that it had no function in anthocyanin production. Furthermore, global analysis of sequences and expression patterns show that the regulatory genes are relatively conserved and might be important in regulating anthocyanin synthesis through different combined expression patterns. To determine the functions of MYB2, 11, and 12, we over-expressed them in petunia and performed yeast two-hybrid analysis with anthocyanin (AN)1 and AN11. The MYB2 protein had strong activity in regulating anthocyanin biosynthesis and induced significant pigment accumulation in transgenic plant petals, whereas MYB11 and MYB12 had lower activities. Our work provided important improvement in the understanding of anthocyanin biosynthesis and established a foundation for floral colour breeding in Phalaenopsis through genetic engineering.     

Chalcone synthase homologous genes cloning and expression pattern in flowering <Emphasis Type="Italic">Fagopyrum tataricum</Emphasis> Gaertn

Tartary buckwheat (Fagopyrum tataricum Gaertn.) is highly nutritious and an excellent dietary source of flavonoid compounds. Chalcone synthase (CHS) is the first key enzyme involved in flavonoid biosynthesis. Here, three putative CHS genes (designated as FtCHS1 (GU172165), FtCHS2 (KT284884), and FtCHS3 (KT284885) were isolated from tartary buckwheat. Nucleotide sequence analysis indicated that FtCHS1 and FtCHS2 each contained one intron of 444 bp and 157 bp, respectively. FtCHS3 included two introns, one of 86 bp and another of 73 bp. The results of quantitative real-time PCR (qRT-PCR) showed the FtCHSs expression presented the same pattern in the stems and flowers, with FtCHS1>FtCHS3>FtCHS2. A different tendency was found in leaves, with FtCHS3>FtCHS2>FtCHS1. However, there was no direct correlation between the three CHS expression and total flavonoids. Furthermore, high-performance liquid chromatography (HPLC) performance reveals rutin is the most abundant flavonoid in all tissues, leaves should be the main location for quercetin storage in tartary buckwheat.     

Constitutive expression of <Emphasis Type="Italic">SlTrxF</Emphasis> increases starch content in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis>

The plastidic thioredoxin F-type (TrxF) protein plays an important role in plant saccharide metabolism. In this study, a gene encoding the TrxF protein, named SlTrxF, was isolated from tomato. The coding region of SlTrxF was cloned into a binary vector under the control of 35S promoter and then transformed into Arabidopsis thaliana. The transgenic Arabidopsis plants exhibited increased starch accumulation compared to the wild-type (WT). Real-time quantitative PCR analysis showed that constitutive expression of SlTrxF up-regulated the expression of ADP-glucose pyrophosphorylase (AGPase) small subunit (AtAGPase-S1 and AtAGPase-S2), AGPase large subunit (AtAGPase-L1 and AtAGPase-L2) and soluble starch synthase (AtSSS I, AtSSS II, AtSSS III and AtSSS IV) genes involved in starch biosynthesis in the transgenic Arabidopsis plants. Meanwhile, enzymatic analyses showed that the major enzymes (AGPase and SSS) involved in the starch biosynthesis exhibited higher activities in the transgenic plants compared to WT. These results suggest that SlTrxF may improve starch content of Arabidopsis by regulating the expression of the related genes and increasing the activities of the major enzymes involved in starch biosynthesis.     

Combining QTL and candidate gene analysis with phenotypic model to unravel the relationship between lodging and related traits in soybean

Lodging is one of the major influencing factors of yield and quality in soybean [Glycine max (L.) Merr.] and other crops. To dissect the genetic basis of lodging in soybean, a recombinant inbred line population consisting of 165 lines was used to evaluate lodging percentage and eight related traits (branch number, internode length, number of nodes, plant height, stem diameter, stem strength, root length, and root weight) in three environments. Regression analysis indicated that plant height and root weight, which explain more than 55% of the variation in lodging percentage, might be the key factors influencing lodging in soybean. Nine consensus quantitative trait locus (QTLs) of lodging percentage were detected in one to three environments. Of which, eight consensus QTLs were colocated with 16 consensus QTLs of lodging-related traits by meta-analysis. In addition, seven candidate genes with the biological functions of shoot branching, root development, internode elongation, and lignin biosynthesis were identified on four pleiotropic QTL regions (oq.13-1, oq.13-2, oq.19-2, and oq.19-3) for lodging percentage and related traits. These findings showed that the consensus QTLs of lodging percentage might result from the pleiotropic QTLs affecting the lodging-related traits. Soybean lodging is determined by the cumulative effect of many traits/processes of growth and development. The combination of MAS, statistical model, and phenotypic selection will provide a powerful breeding strategy for lodging resistance in soybean.     

Nitrogen fertilizer application affects lodging resistance by altering secondary cell wall synthesis in japonica rice (<Emphasis Type="Italic">Oryza sativa</Emphasis>)

Stem mechanical strength is an important agricultural quantitative trait that is closely related to lodging resistance in rice, which is known to be reduced by fertilizer with higher levels of nitrogen. To understand the mechanism that regulates stem mechanical strength in response to nitrogen, we analysed stem morphology, anatomy, mechanical properties, cell wall components, and expression of cell wall-related genes, in two varieties of japonica rice, namely, Wuyunjing23 (lodging-resistant variety) and W3668 (lodging-susceptible variety). The results showed that higher nitrogen fertilizer increased the lodging index in both varieties due to a reduction in breaking strength and bending stress, and these changes were larger in W3668. Cellulose content decreased slightly under higher nitrogen fertilizer, whereas lignin content reduced remarkably. Histochemical staining revealed that high nitrogen application decreased lignin deposition in the secondary cell wall of the sclerenchyma cells and vascular bundle cells compared with the low nitrogen treatments, while it did not alter the pattern of cellulose deposition in these cells in both Wuyunjing23 and W3668. In addition, the expression of the genes involved in lignin biosynthesis, OsPAL, OsCoMT, Os4CL3, OsCCR, OsCAD2, OsCAD7, OsCesA4, and OsCesA7, were also down-regulated under higher nitrogen conditions at the early stage of culm growth. These results suggest that the genes involved in lignin biosynthesis are down-regulated by higher nitrogen fertilizer, which causes lignin deficiency in the secondary cell walls and the weakening of mechanical tissue structure. Subsequently, this results in these internodes with reduced mechanical strength and poor lodging resistance.     

Changes in the expression of key genes involved in the biosynthesis of menthol and menthofuran in <Emphasis Type="Italic">Mentha piperita</Emphasis> L. under drought stress

Peppermint (Mentha piperita) is known as an important medicinal plant throughout the world. In the present study, after exposing peppermint plants under drought stress, the qRT-PCR was use to analyze the expression of genes involved in menthol biosynthesis pathway and encoding: limonene synthase (lS), limon-3-hydroxylase (l3oh), trans-isopiperitenol dehydrogenase (ipd), isopiperitenone reductase (ipr), pulegone reductase (pr), menthol dehydrogenase (mdeh), and menthofuran synthase (mfs), which also evaluated the morphological and physiological traits. The results revealed that due to water stress, the gene expression levels of ipd, ipr, and mfs were increased, whereas the gene expression level of pr and mdeh was decreased under water stress conditions. The most of essential oil components (menthol, menthofuran, and plugene), which were analyzed by gas chromatography–mass spectrometry (GC–MS), was positively correlated with genes expression. Drought stress decreased morphological and induces increasing contents of pulegone and menthofuran and reduction in menthol percentages. Results from this study suggest that up-regulation of mfs might contribute to the altered of menthofuran as well as down-regulation of mdeh might cause the reduction of menthol. Furthermore, increasing ls gene expression levels might induce more essential oil yield, while reduction of mfs gene expression levels causes an improvement of essential oil quality.