The central regulator of the ethylene (ET) signaling pathway, which controls a plethora of developmental programs and responses to environmental cues in plants, is ETHYLENE-INSENSITIVE2 (EIN2). Here we identify a chromatin-dependent regulatory mechanism at EIN2 requiring two genes: ETHYLENE-INSENSITIVE6 (EIN6), which is a H3K27me3 demethylase also known as RELATIVE OF EARLY FLOWERING6 (REF6), and EIN6 ENHANCER (EEN), the Arabidopsis homolog of the yeast INO80 chromatin remodeling complex subunit IES6 (INO EIGHTY SUBUNIT). Strikingly, EIN6 (REF6) and the INO80 complex redundantly control the level and the localization of the repressive histone modification H3K27me3 and the histone variant H2A.Z at the 5’ untranslated region (5’UTR) intron of EIN2. Concomitant loss of EIN6 (REF6) and the INO80 complex shifts the chromatin landscape at EIN2 to a repressive state causing a dramatic reduction of EIN2 expression. These results uncover a unique type of chromatin regulation which safeguards the expression of an essential multifunctional plant stress regulator.

L'invention concerne l'acide nucleique et des sequences de polypeptides qui concernent un gene EIN6, gene implique dans la reponse des plantes a l'ethylene. L'invention traite de vecteurs de transformation de plantes et de plantes transgeniques qui presentent un phenotype dependant de l'ethylene altere en raison de l'expression alteree de l'EIN6 dans les plantes transformees.

The expression of CHALCONE SYNTHASE(CHS) expression is an important control step in the biosynthesis of flavonoids, which are major photoprotectants in plants. CHS transcription is regulated by endogenous programs and in response to environmental signals. Luciferase reporter gene fusions showed that the CHS promoter is controlled by the circadian clock both in roots and in aerial organs of transgenic Arabidopsis plants. The period of rhythmicCHS expression differs from the previously described rhythm of chlorophyll a/b-binding protein (CAB) gene expression, indicating thatCHS is controlled by a distinct circadian clock. The difference in period is maintained in the wild-type Arabidopsis accessions tested and in the de-etiolated 1 andtiming of CAB expression 1 mutants. These clock-affecting mutations alter the rhythms of both CABand CHS markers, indicating that a similar (if not identical) circadian clock mechanism controls these rhythms. The distinct tissue distribution of CAB andCHS expression suggests that the properties of the circadian clock differ among plant tissues. Several animal organs also exhibit heterogeneous circadian properties in culture but are believed to be synchronized in vivo. The fact that differing periods are manifest in intact plants supports our proposal that spatially separated copies of the plant circadian clock are at most weakly coupled, if not functionally independent. This autonomy has apparently permitted tissue-specific specialization of circadian timing.

Ethylene is a plant hormone that regulates a diverse set of developmental and physiological processes including seed germination, abscission, and senescence. Molecular genetic analysis of ethylene signaling in Arabidopsis thaliana, has led to the identification of a number of genetic loci that are required for normal ethylene responses. Cloning of several of the mutant loci has provided significant insight into the nature of the ethylene signaling pathway. The Raf kinase homolog CTR1 is predicted to negatively regulate the ethylene response pathway through a MAP kinase cascade. ETR1 has been demonstrated to bind ethylene, and a family of homologous genes encode products that may function in a receptor complex. EIN3 and three homologous gene products contain several protein motifs that are reminiscent of transcription factors, and transduce the ethylene signal downstream. Additional loci are defined by the ein2, ein5/ain1, ein6, and ein7 mutations, and a number of mutations defining tissue-specific mediators of ethylene responses have also been identified. In this review, the different ethylene-related mutations and their gene products are considered in detail, and possible models of the manner in which the pathway functions are proposed. (C) Elsevier, Paris.

Light signal-transduction pathways are a central component of the mechanisms that regulate plant development. These pathways provide the means by which information from specific wavelengths of light may be amplified and coordinated, resulting in complex physiological and developmental responses. This review focuses upon recent approaches towards establishing the intermediates that transmit signals from photoreceptors, phytochromes in particular, to target elements in the promoters of light-regulated genes.

and there is increasing evidence of links between diet, metabolism, and the clock (28, 29). Similarly , our data show that in plants a photosynthesis-related signal, possibly sucrose or a derivative, can affect setting of the clock in roots but not in shoots. In summary, the plant clock is organ-specific but not organ-autonomous. Diversity in leaf shape is produced by alterations of the margin: for example, deep dissection leads to leaflet formation and less-pronounced incision results in serrations or lobes. By combining gene silencing and mutant analyses in four distantly related eudicot species, we show that reducing the function of NAM/CUC boundary genes (NO APICAL MERISTEM and CUP-SHAPED COTYLEDON) leads to a suppression of all marginal outgrowths and to fewer and fused leaflets. We propose that NAM/CUC genes promote formation of a boundary domain that delimits leaflets. This domain has a dual role promoting leaflet separation locally and leaflet formation at distance. In this manner, boundaries of compound leaves resemble boundaries functioning during animal development. L eaves of seed plants can be simple, with a single leaf blade, or compound when divided into distinct leaflets (1, 2). Additionally , margins of both simple and compound leaves can elaborate less-pronounced incisions such as serrations or lobes. Regardless of the final shape, leaves are initiated as simple primordia from the shoot apical meristem. Primordia of compound leaves maintain an organogenic region at their margin from which leaflet primordia emerge (1, 2). Two different pathways have been recruited to promote this organogenic activity during the multiple independent origins of compound leaves in seed plants. One pathway involves expression in the primordia of compound leaves of class 1 homeodomain KNOTTED1– like (KNOXI) transcription factors that were initially identified for their role in maintenance of meristem identity (3–5). This pathway is active in a wide range of flowering seed plants, including Solanum lycopersicum and Cardamine hirsuta. A second pathway involving the UNIFOLIATA (UNI) gene is found in Pisum sativum, which does not express KNOXI genes in the leaf pri-mordium. UNI encodes a member of the LEAFY (LFY) family of transcription factors, initially identified for its role in floral meristem identity (6, 7). Despite progress in understanding what promotes the organogenic potential of compound leaves, the mechanistic basis of leaflet formation and delimitation is less clear. The generation of activity maxima of auxin, a small indolic hormone, is one such mechanism that facilitates initiation and separation …