Flower Development and Photoperiodic Control of Flowering in Rice

Floral transition,which is referred to as a plant＇s transition from vegetative stage to reproductive stage,is considered to be a critical developmental switch in higher plants,for a timely flowering is a major factor of reproductive success.Endogenous and environmental cues,such as photoperiod,light quality,plant hormones concentrations and temperature,provide information to the plants whether the environment is favorable for flowering.These cues promote,or prevent,flowering through a complex genetic network,mediated by a careful orchestration of temporal and spatial gene expression.One of such cues is photoperiod.Rice（Oryza sativa L.） serves as a powerful model species for the understanding of flowering in higher plants,including flower development and photoperiodic control of flowering.In this review,we overviewed and discussed the flower development and its model.We also overviewed the photoperiodic pathways in rice flowering control,and summarized the pathways at molecular level.

Flavonoid content and expression analysis of flavonoid biosynthetic genes in herbaceous peony(Paeonia lactiflora Pall.)with double colors

Herbaceous peony（Paeonia lactiflora Pall.） is a famous flower with medicinal values, and its flowers have a number of medicinal constituents, especially flavonoids. In this study, a P. lactiflora cultivar with double colors including white outer-petal and yellow inner-petal was used as the experimental materials to perform the qualitative and quantitative analysis of flavonoids by high-performance liquid chromatograph-electrospray ionization-mass spectrometry（HPLC-ESI-MSn） and investigate the expression patterns of flavonoid biosynthetic genes using real-time quantitative polymerase chain reaction（Q-PCR）. The results showed that the colors of both petals gradually weakened with flower development. Moreover, one main anthocyanin composition（peonidin 3,5-di-O-glucoside） and five main anthoxanthin compositions（kaempferol di-hexoside, kaempferol-3-O-malonylglucoside-7-O-glucoside, quercetin-3-O-galactoside, luteolin-7-O-glucoside and isorhamnetin-3-O-glucoside） were found in the both, differing significantly in their peak areas only. Total anthocyanin, anthoxanthin and flavonoid contents in white outer-petal and yellow inner-petal gradually decreased during flower development, and were consistently higher in white outer-petal. Furthermore, the expression patterns of nine structural genes in P. lactiflora flavonoid biosynthetic pathway showed that the expression levels of phenylalanine ammonialyase gene（Pl PAL）, chalcone synthase gene（PlC HS）, flavanone 3-hydroxylase gene（PlF 3H）, anthocyanidin synthase gene（PlA NS） and UDP-glucoside： flavonoid 5-O-glucosyltransferase gene（Pl F5GT） in two petals basically presented declined tendencies, and transcription levels of Pl PAL, Pl CHS, Pl ANS, Pl F3 GT and Pl F5 GT also tended to be higher in white outer-petal, which was correlated with their flavonoid contents. These results would lay a solid foundation for the exploration and utilization of flavonoid resources in P. lactiflora flowers.

Analysis of Gene Networks for Arabidopsis Flowering

The flowering time of Arabidopsis is sensitive to climate variability, with lighting conditions being a major determinant of the flowering time. Long-days induce early flowering, while short-days induce late flowering or even no flowers. This study investigates the intrinsic mechanisms for Arabidopsis flowering in different lighting conditions using mutual information networks and logic networks. The structure parameters of the mutual information networks show that the average degree and the average core clearly distinguish these networks. A method is then given to find the key structural genes in the mutual information networks and the logic networks respectively. Ten genes are found to possibly promote flowering with three genes that may restrain flowering. The sensitivity of this method to find the genes that promote flowering is 80%, while the sensitivity of the method to find the genes that restrain flowering is 100%.

Transcriptome analysis of Saposhnikovia divaricata and mining of bolting and fowering genes

Objective: Early bolting of Saposhnikovia divaricata has seriously hindered its medicinal value and sustainable development of resources. The molecular mechanism of bolting and fowering of S. divaricata is still unclear and worth of research. In our study, we explored the transcriptome of the genes related to the bolting and fowering of S. divaricata.Methods: The transcriptome library was constructed, sequenced, assembled and annotated from the bolting and unbolting leaves of S. divaricata by high-throughput sequencing at the bud and fowering stage.Focus on the pathways related to bolting and fowering in plants, and exploring genes. The expression of seven candidate genes was verified by real-time fuorescence quantitative PCR(qRT-PCR).Results: Transcriptome results showed that 249 889 422 high-quality clean reads were obtained. A total of 67 866 unigenes were assembled with an average length of 948.1 bp. Trinity de Novo assembly produced 67 866 unigenes with an average length of 948.1 bp. Among 993 differentially expressed genes,484 genes were significantly up-regulated and 509 genes were down-regulated in the SdM group. A total of 79 GO terms were significantly enriched for differentially expressed genes. KEGG results showed that 11 154 unigenes were enriched in 89 pathways. And 21 candidate genes related to bolting and fowering of S. divaricata were excavated. The qRT-PCR results showed that expression trends of HDA9, PHYB, AP2,TIR1, Hsp90, CaM, and IAA7 were consistent with transcriptomic sequencing results. In addition, RNA-seq had identified 10 740 transcription factors and classified them into 58 families by their conserved domains. Further studies showed that the transcription factors regulating the fowering of S. divaricata were mainly distributed in the NAC, MYB_related, HB-other, ARF, and AP2 families.Conclusion: Based on the results of this study, it was found that the plant hormone signal transduction pathway was one of the decisive factors to control bolting and fowering. Among them, auxin related genes IAA and TIR1 are the key genes in the bolting and fowering process of S. divaricata.

Nonfunctional alleles of long-day suppressor genes independently regulate flowering time

Due to the remarkable adaptability to various environments, rice varieties with diverse flowering times have abeen domesticated or improved from Oryza rufipogon.Detailed knowledge of the genetic factors controlling flowering time will facilitate understanding the adaptation mechanism in cultivated rice and enable breeders to design appropriate genotypes for distinct preferences. In this study,four genes（Hd1, DTH8, Ghd7 and OsPRR37） in a rice long-day suppression pathway were collected and sequenced in 154, 74,69 and 62 varieties of cultivated rice（Oryza sativa）respectively. Under long-day conditions, varieties with nonfunctional alleles flowered significantly earlier than those with functional alleles. However, the four genes have different genetic effects in the regulation of flowering time： Hd1 and Os PRR37 are major genes that generally regulate rice flowering time for all varieties, while DTH8 and Ghd7 only regulate regional rice varieties. Geographic analysis and network studies suggested that the nonfunctional alleles of these suppression loci with regional adaptability were derived recently and independently. Alleles with regional adaptability should be taken into consideration for genetic improvement. The rich genetic variations in these four genes,which adapt rice to different environments, provide the flexibility needed for breeding rice varieties with diverse flowering times.

Graft-accelerated virus-induced gene silencing facilitates functional genomics in rose flowers

Rose has emerged as a model ornamental plant for studies of flower development, senescence, and morphology, as well as the metabolism of floral fragrances and colors.Virus-induced gene silencing(VIGS) has long been used in functional genomics studies of rose by vacuum infiltration of cuttings or seedlings with an Agrobacterium suspension carrying TRV-derived vectors. However, VIGS in rose flowers remains a challenge because of its low efficiency and long time to establish silencing. Here we present a novel and rapid VIGS method that can be used to analyze gene function in rose,called ‘graft-accelerated VIGS’, where axil ary sprouts are cut from the rose plant and vacuum infiltrated with Agrobacterium. The inoculated scions are then grafted back onto the plants to flower and silencing phenotypes can be observed within 5 weeks, post-infiltration. Using this new method, we successfully silenced expression of the RhDFR, RhA G, and RhNUDXin rose flowers, and affected their color, petal number, as well as fragrance, respectively. This grafting method will facilitate high-throughput functional analysis of genes in rose flowers. Importantly, it may also be applied to other woody species that are not currently amenable to VIGS by conventional leaf or plantlet/seedling infiltration methods.

Temporal and Spatial Requirement of EMF1 Activity for Arabidopsis Vegetative and Reproductive Development

EMBRYONIC FLOWER （EMF） genes are required to maintain vegetative development via repression of flower homeotic genes in Arabidopsis. Removal of EMF gene function caused plants to flower upon germination, producing abnormal and sterile flowers. The pleiotropic effect of ernfl mutation suggests its requirement for gene programs involved in diverse developmental processes. Transgenic plants harboring EMF1 promoter：：glucuronidase （GUS） reporter gene were generated to investigate the temporal and spatial expression pattern of EMF1. These plants displayed differential GUS activity in vegetative and flower tissues, consistent with the role of EMF1 in regulating multiple gene programs. EMFI：：GUS expression pattern in emf mutants suggests organ-specific auto-regulation. Sense- and antisense （as） EMF1 cDNA were expressed under the control of stage- and tissue-specific promoters in transgenic plants. Characterization of these transgenic plants showed that EMF1 activity is required in meristematic as well as differentiating tissues to rescue emf mutant phenotype. Temporal removal or reduction of EMF1 activity in the embryo or shoot apex of wild-type seedlings was sufficient to cause early flowering and terminal flower formation in adult plants. Such reproductive cell memory is reflected in the flower MADS-box gene activity expressed prior to flowering in these early flowering plants. However, temporal removal of EMF1 activity in flower meristem did not affect flower development. Our results are consistent with EMF1＇s primary role in repressing flowering in order to allow for vegetative growth.