It's time to flower: the genetic control of flowering time

In plants, successful sexual reproduction and the ensuing development of seeds and fruits depend on flowering at the right time. This involves coordinating flowering with the appropriate season and with the developmental history of the plant. Genetic and molecular analysis in the small cruciform weed, Arabidopsis, has revealed distinct but linked pathways that are responsible for detecting the major seasonal cues of day length and cold temperature, as well as other local environmental and internal signals. The balance of signals from these pathways is integrated by a common set of genes to determine when flowering occurs. Excitingly, it has been discovered that many of these same genes regulate flowering in other plants, such as rice. This review focuses on recent advances in how three of the signalling pathways (the day-length, vernalisation and autonomous pathways) function to control flowering.     

Understanding the genetic and epigenetic architecture in complex network of rice flowering pathways

Although the molecular basis of flowering time control is well dissected in the long day (LD) plant Arabidopsis, it is still largely unknown in the short day (SD) plant rice. Rice flowering time (heading date) is an important agronomic trait for season adaption and grain yield, which is affected by both genetic and environmental factors. During the last decade, as the nature of florigen was identified, notable progress has been made on exploration how florigen gene expression is genetically controlled. In Arabidopsis expression of certain key flowering integrators such as FLOWERING LOCUS C (FLC) and FLOWERING LOCUS T (FT) are also epigenetically regulated by various chromatin modifications, however, very little is known in rice on this aspect until very recently. This review summarized the advances of both genetic networks and chromatin modifications in rice flowering time control, attempting to give a complete view of the genetic and epigenetic architecture in complex network of rice flowering pathways.     

APETALA1 and SEPALLATA3 interact to promote flower development

In Arabidopsis, the closely related APETALA1 (AP1) and CAULIFLOWER (CAL) MADS-box genes share overlapping roles in promoting flower meristem identity. Later in flower development, the AP1 gene is required for normal development of sepals and petals. Studies of MADS-domain proteins in diverse species have shown that they often function as heterodimers or in larger ternary complexes, suggesting that additional proteins may interact with AP1 and CAL during flower development. To identify proteins that may interact with AP1 and CAL, we used the yeast two-hybrid assay. Among the five MADS-box genes identified in this screen, the SEPALLATA3 (SEP3) gene was chosen for further study. Mutations in the SEP3 gene, as well as SEP3 antisense plants that have a reduction in SEP3 RNA, display phenotypes that closely resemble intermediate alleles of AP1. Furthermore, the early flowering phenotype of plants constitutively expressing AP1 is significantly enhanced by constitutive SEP3 expression. Taken together, these studies suggest that SEP3 interacts with AP1 to promote normal flower development.     

Regulatory networks of non-coding RNAs in brown/beige adipogenesis

BAT (brown adipose tissue) is specialized to burn fatty acids for heat generation and energy expenditure to defend against cold and obesity. Accumulating studies have demonstrated that manipulation of BAT activity through various strategies can regulate metabolic homoeostasis and lead to a healthy phenotype. Two classes of ncRNA (non-coding RNA), miRNA and lncRNA (long non-coding RNA), play crucial roles in gene regulation during tissue development and remodelling. In the present review, we summarize recent findings on regulatory role of distinct ncRNAs in brown/beige adipocytes, and discuss how these ncRNA regulatory networks contribute to brown/beige fat development, differentiation and function. We suggest that targeting ncRNAs could be an attractive approach to enhance BAT activity for protecting the body against obesity and its pathological consequences.     

Pollinator conservation at the local scale: flower density,diversity and community structure increase flower visiting insect activity to mixed floral stands

Insect pollinators play a keystone role in terrestrial ecosystems. The parallel declines in plant and pollinator communities emphasizes that plant-pollinator interactions at the community level are highly relevant for biodiversity conservation. Here we examine relationships between plants and flower-visiting insects (anthophiles) at the scale of local floral patches. We conducted a visitation survey during the spring flowering season, a peak time for pollinator activity in the threatened Cape Floristic Region, South Africa. We tested floral density, diversity and composition as predictors of anthophile diversity (measured at the family/family group level) and visitation rates in multispecies stands of flowers. Although different anthophile groups responded differently, generally anthophile visitation rates and diversity were positively affected by floral density, diversity and community structure. Anthophiles were more abundant and diverse in areas with a high density and diversity of flowers. Plant community structure affected both the likelihood of occurrence and activity of anthophiles in the plots. The two mass flowering species examined here, Relhania fruticosa and Salvia chamaeleagnea, were strong determinants of anthophile activity, greatly increasing visitation rates, even though there was, on average, lower floral density and diversity. Our results show that anthophile activity is affected by highly localised, small-scale factors, namely the density and diversity of flowers and community structure. Important among these factors are patches of high quality habitat, high in floral abundance and diversity, both of which should be included in landscape-level plans for pollinator conservation, providing stepping stones for these insects in transformed landscapes.     

长链非编码RNA与表观遗传调控

近年来,表观遗传学(epigenetics)备受关注.表观遗传调控的方式主要包括DNA甲基化、组蛋白修饰和染色质重塑等.ENCODE计划及随后的研究发现,人类基因组中仅有很小一部分DNA序列负责编码蛋白质,而其余大部分被转录为非编码RNA(non-codingRNA,ncRNA).其中长链非编码RNA(long non-codingRNA,lncRNA)是一类长度大于200nt并且缺乏蛋白质编码能力的RNA分子.越来越多的研究表明,lncRNAs能够通过表观遗传调控、转录调控以及转录后调控等多个层面调节基因的表达,从而参与细胞增殖、分化和凋亡等多种生物学过程.本文将着重综述lncRNAs在表观遗传调控中的作用及其最新的研究进展.     

ADAR-mediated RNA editing in non-coding RNA sequences

Adenosine to inosine (A-to-I) RNA editing is the most abundant editing event in animals. It converts adenosine to inosine in double-stranded RNA regions through the action of the adenosine deaminase acting on RNA (ADAR) proteins. Editing of pre-mRNA coding regions can alter the protein codon and increase functional diversity. However, most of the A-to-I editing sites occur in the non-coding regions of pre-mRNA or mRNA and non-coding RNAs. Untranslated regions (UTRs) and introns are located in pre-mRNA non-coding regions, thus A-to-I editing can influence gene expression by nuclear retention, degradation, alternative splicing, and translation regulation. Non-coding RNAs such as microRNA (miRNA), small interfering RNA (siRNA) and long non-coding RNA (lncRNA) are related to pre-mRNA splicing, translation, and gene regulation. A-to-I editing could therefore affect the stability, biogenesis, and target recognition of non-coding RNAs. Finally, it may influence the function of non-coding RNAs, resulting in regulation of gene expression. This review focuses on the function of ADAR-mediated RNA editing on mRNA non-coding regions (UTRs and introns) and non-coding RNAs (miRNA, siRNA, and lncRNA).     

Mechanisms and function of flower and inflorescence reversion

Flower and inflorescence reversion involve a switch from floral development back to vegetative development, thus rendering flowering a phase in an ongoing growth pattern rather than a terminal act of the meristem. Although it can be considered an unusual event, reversion raises questions about the nature and function of flowering. It is linked to environmental conditions and is most often a response to conditions opposite to those that induce flowering. Research on molecular genetic mechanisms underlying plant development over the last 15 years has pinpointed some of the key genes involved in the transition to flowering and flower development. Such investigations have also uncovered mutations which reduce floral maintenance or alter the balance between vegetative and floral features of the plant. How this information contributes to an understanding of floral reversion is assessed here. One issue that arises is whether floral commitment (defined as the ability to continue flowering when inductive conditions no longer exist) is a developmental switch affecting the whole plant or is a mechanism which assigns autonomy to individual meristems. A related question is whether floral or vegetative development is the underlying default pathway of the plant. This review begins by considering how studies of flowering in Arabidopsis thaliana have aided understanding of mechanisms of floral maintenance. Arabidopsis has not been found to revert to leaf production in any of the conditions or genetic backgrounds analysed to date. A clear-cut reversion to leaf production has, however, been described in Impatiens balsamina. It is proposed that a single gene controls whether Impatiens reverts or can maintain flowering when inductive conditions are removed, and it is inferred that this gene functions to control the synthesis or transport of a leaf-generated signal. But it is also argued that the susceptibility of Impatiens to reversion is a consequence of the meristem-based mechanisms controlling development of the flower in this species. Thus, in Impatiens, a leaf-derived signal is critical for completion of flowering and can be considered to be the basis of a plant-wide floral commitment that is achieved without accompanying meristem autonomy. The evidence, derived from in vitro and other studies, that similar mechanisms operate in other species is assessed. It is concluded that most species (including Arabidopsis) are less prone to reversion because signals from the leaf are less ephemeral, and the pathways driving flower development have a high level of redundancy that generates meristem autonomy even when leaf-derived signals are weak. This gives stability to the flowering process, even where its initiation is dependent on environmental cues. On this interpretation, Impatiens reversion appears as an anomaly resulting from an unusual combination of leaf signalling and meristem regulation. Nevertheless, it is shown that the ability to revert can serve a function in the life history strategy (perenniality) or reproductive habit (pseudovivipary) of many plants. In these instances reversion has been assimilated into regular plant development and plays a crucial role there.