Interpreting Cytokinin Action as Anterograde Signaling and Beyond

Among the major phytohormones, the cytokinin exhibits unique features for its ability to positively affect the developmental status of plastids. Even early on in its research, cytokinins were known to promote plastid differentiation and to reduce the loss of chlorophyll in detached leaves. Since the discovery of the components of cytokinin perception and primary signaling, the genes involved in photosynthesis and plastid differentiation have been identified as those directly targeted by type-B response regulators. Furthermore, cytokinins are known to modulate versatile cellular processes such as promoting the division and differentiation of cells and, in concert with auxin, initiating the de novo formation of shoot apical meristem (SAM) in tissue cultures. Yet how cytokinins precisely participate in such diverse cellular phenomena, and how the associated cellular processes are coordinated as a whole, remains unclear. A plausible presumption that would account for the coordinated gene expression is the tight and reciprocal communication between the nucleus and plastid. The fact that cytokinins affect plastid developmental status via gene expression in both the nucleus and plastid is interpreted here to suggest that cytokinin functions as an initiator of anterograde (nucleus-to-plastid) signaling. Based on this viewpoint, we first summarize the physiological relevance of cytokinins to the coordination of plastid differentiation with de novo shoot organogenesis in tissue culture systems. Next, the role of endogenous cytokinins in influencing plastid differentiation within the SAM of intact plants is discussed. Finally, a presumed plastid-derived signal in response to cytokinins for coupled nuclear gene expression is proposed

Novel Cytokinin Derivatives Do Not Show Negative Effects on Root Growth and Proliferation in Submicromolar Range

BACKGROUND: When applied to a nutrition solution or agar media, the non-substituted aromatic cytokinins caused thickening and shortening of the primary root, had an inhibitory effect on lateral root branching, and even showed some negative effects on development of the aerial part at as low as a 10 nanomolar concentration. Novel analogues of aromatic cytokinins ranking among topolins substituted on N9-atom of adenine by tetrahydropyranyl or 4-chlorobutyl group have been prepared and tested in standardized cytokinin bioassays [1]. Those showing comparable activities with N(6)-benzylaminopurine were further tested in planta. METHODOLOGY/PRINCIPAL FINDINGS: The main aim of the study was to explain molecular mechanism of function of novel cytokinin derivatives on plant development. Precise quantification of cytokinin content and profiling of genes involved in cytokinin metabolism and perception in treated plants revealed several aspects of different action of m-methoxytopolin base and its substituted derivative on plant development. In contrast to standard cytokinins, N9- tetrahydropyranyl derivative of m-topolin and its methoxy-counterpart showed the negative effects on root development only at three orders of magnitude higher concentrations. Moreover, the methoxy-derivative demonstrates a positive effect on lateral root branching and leaf emerging in a nanomolar range of concentrations, in comparison with untreated plants. CONCLUSIONS/SIGNIFICANCE: Tetrahydropyranyl substitution at N9-position of cytokinin purine ring significantly enhances acropetal transport of a given cytokinins. Together with the methoxy-substitution, impedes accumulation of non-active cytokinin glucoside forms in roots, allows gradual release of the active base, and has a significant effect on the distribution and amount of endogenous isoprenoid cytokinins in different plant tissues. The utilization of novel aromatic cytokinin derivatives can distinctively improve expected hormonal effects in plant propagation techniques in the future

Ecouniversity for Children

ústav navrhování I

First Come, First Served: Sui Generis Features of the First Intron

Most of the transcribed genes in eukaryotic cells are interrupted by intervening sequences called introns that are co-transcriptionally removed from nascent messenger RNA through the process of splicing. In Arabidopsis, 79% of genes contain introns and more than 60% of intron-containing genes undergo alternative splicing (AS), which ostensibly is considered to increase protein diversity as one of the intrinsic mechanisms for fitness to the varying environment or the internal developmental program. In addition, recent findings have prevailed in terms of overlooked intron functions. Here, we review recent progress in the underlying mechanisms of intron function, in particular by focusing on unique features of the first intron that is located in close proximity to the transcription start site. The distinct deposition of epigenetic marks and nucleosome density on the first intronic DNA sequence, the impact of the first intron on determining the transcription start site and elongation of its own expression (called intron-mediated enhancement, IME), translation control in 5′-UTR, and the new mechanism of the trans-acting function of the first intron in regulating gene expression at the post-transcriptional level are summarized

Interpreting Cytokinin Action as Anterograde Signaling and Beyond

Among the major phytohormones, the cytokinin exhibits unique features for its ability to positively affect the developmental status of plastids. Even early on in its research, cytokinins were known to promote plastid differentiation and to reduce the loss of chlorophyll in detached leaves. Since the discovery of the components of cytokinin perception and primary signaling, the genes involved in photosynthesis and plastid differentiation have been identified as those directly targeted by type-B response regulators. Furthermore, cytokinins are known to modulate versatile cellular processes such as promoting the division and differentiation of cells and, in concert with auxin, initiating the de novo formation of shoot apical meristem (SAM) in tissue cultures. Yet how cytokinins precisely participate in such diverse cellular phenomena, and how the associated cellular processes are coordinated as a whole, remains unclear. A plausible presumption that would account for the coordinated gene expression is the tight and reciprocal communication between the nucleus and plastid. The fact that cytokinins affect plastid developmental status via gene expression in both the nucleus and plastid is interpreted here to suggest that cytokinin functions as an initiator of anterograde (nucleus-to-plastid) signaling. Based on this viewpoint, we first summarize the physiological relevance of cytokinins to the coordination of plastid differentiation with de novo shoot organogenesis in tissue culture systems. Next, the role of endogenous cytokinins in influencing plastid differentiation within the SAM of intact plants is discussed. Finally, a presumed plastid-derived signal in response to cytokinins for coupled nuclear gene expression is proposed

Interpreting Cytokinin Action as Anterograde Signaling and Beyond

Among the major phytohormones, the cytokinin exhibits unique features for its ability to positively affect the developmental status of plastids. Even early on in its research, cytokinins were known to promote plastid differentiation and to reduce the loss of chlorophyll in detached leaves. Since the discovery of the components of cytokinin perception and primary signaling, the genes involved in photosynthesis and plastid differentiation have been identified as those directly targeted by type-B response regulators. Furthermore, cytokinins are known to modulate versatile cellular processes such as promoting the division and differentiation of cells and, in concert with auxin, initiating the de novo formation of shoot apical meristem (SAM) in tissue cultures. Yet how cytokinins precisely participate in such diverse cellular phenomena, and how the associated cellular processes are coordinated as a whole, remains unclear. A plausible presumption that would account for the coordinated gene expression is the tight and reciprocal communication between the nucleus and plastid. The fact that cytokinins affect plastid developmental status via gene expression in both the nucleus and plastid is interpreted here to suggest that cytokinin functions as an initiator of anterograde (nucleus-to-plastid) signaling. Based on this viewpoint, we first summarize the physiological relevance of cytokinins to the coordination of plastid differentiation with de novo shoot organogenesis in tissue culture systems. Next, the role of endogenous cytokinins in influencing plastid differentiation within the SAM of intact plants is discussed. Finally, a presumed plastid-derived signal in response to cytokinins for coupled nuclear gene expression is proposed

Maize cytokinin dehydrogenase isozymes are predominantly localized to the vacuole

The maize genome encompasses 13 genes encoding for cytokinin dehydrogenase isozymes (CKXs). These enzymes are responsible for irreversible degradation of cytokinin plant hormones and thus, contribute regulating their levels. Here, we focus on the unique aspect of CKXs: their diverse subcellular distribution, important in regulating cytokinin homeostasis. Maize CKXs were tagged with green fluorescent protein (GFP) and transiently expressed in maize protoplasts. Most of the isoforms, namely ZmCKX1, ZmCKX2, ZmCKX4a, ZmCKX5, ZmCKX6, ZmCKX8, ZmCKX9, and ZmCKX12, were associated with endoplasmic reticulum (ER) several hours after transformation. GFP-fused CKXs were observed to accumulate in putative prevacuolar compartments. To gain more information about the spatiotemporal localization of the above isoforms, we prepared stable expression lines of all ZmCKX–GFP fusions in Arabidopsis thaliana Ler suspension culture. All the ER-associated isoforms except ZmCKX1 and ZmCKX9 were found to be targeted primarily to vacuoles, suggesting that ER-localization is a transition point in the intracellular secretory pathway and vacuoles serve as these isoforms’ final destination. ZmCKX9 showed an ER-like localization pattern similar to those observed in the transient maize assay. Apoplastic localizations of ZmCKX1 was further confirmed and ZmCKX10 showed cytosolic/nuclear localization due to the absence of the signal peptide sequence as previously reported. Additionally, we prepared GFP-fused N-terminal signal deletion mutants of ZmCKX2 and ZmCKX9and clearly demonstrated that the localization pattern of these mutant forms was cytosolic/nuclear. This study provides the first complex model for spatiotemporal localization of the key enzymes of the cytokinin degradation/catabolism in monocotyledonous plants

Analysis of the ploidy of the epidermal cells of the hypocotyl of cv. Rutgers and the <i>7B-1</i> mutant after 5 days of growth in the D or in continuous BL (10 µmol.m

<p>^−<b>2</b><b>.s</b>^−<b>1</b><b>).</b> Results represent averages ± SE (n = 10). a: significantly different from the D condition; b: significantly different from cv. Rutgers grown in the same condition (two-way ANOVA, Bonferroni <i>post-hoc</i> test, p<0.05).</p

Analysis by qRT-PCR of the expression of four <i>LOG</i> genes of tomato in the upper part of the hypocotyl of cv. Rutgers seedlings grown for 2 days in the D then transferred to continuous BL (10 µmol.m

<p>^−<b>2</b><b>.s</b>^−<b>1</b><b>).</b> Results represent the averages ± SE of 3 independent biological repeats. The <i>EF1α</i> gene was taken as housekeeping gene. The relative expression was made against the expression of <i>SlLOG1</i> gene in the 2 day-old seedlings unexposed to BL. a: the expression of <i>SlLOG1</i> gene is significantly different from the expression in the 2 do seedlings unexposed to BL; b: the expression of <i>SlLOG6</i> gene is significantly different from the expression in the 2 do seedlings unexposed to BL (one-way ANOVA, Bonferroni post-hoc: p<0.05). The frame represents the data obtained for <i>SlLOG2</i> gene in the 3 independent biological repeats, showing the same trends despite the variability between repeats.</p

Analysis by qRT-PCR of the expression of two <i>CKX</i> genes of tomato in the hypocotyl of cv. Rutgers and <i>7B-1</i> seedlings grown for 2 days in the D (0

<p> <b>h BL) and transferred for 24 </b><b>h in continuous BL (10 µmol.m</b>^−<b>2</b><b>.s</b>^−<b>1</b><b>; 24 </b><b>h BL).</b> Results represent averages ± SE of three independent biological repeat. The EF1α gene was taken as housekeeping gene. The relative quantification was made against the expression of <i>SlLOG1</i> from the sample ‘0 h BL cv. Rutgers’. A two-way ANOVA with Bonferroni post-test was performed, taking separately each gene; no significant difference was observed.</p