TY - JOUR AB - Plant embryogenesis is regulated by differential distribution of the plant hormone auxin. However, the cells establishing these gradients during microspore embryogenesis remain to be identified. For the first time, we describe, using the DR5 or DR5rev reporter gene systems, the GFP- and GUS-based auxin biosensors to monitor auxin during Brassica napus androgenesis at cellular resolution in the initial stages. Our study provides evidence that the distribution of auxin changes during embryo development and depends on the temperature-inducible in vitro culture conditions. For this, microspores (mcs) were induced to embryogenesis by heat treatment and then subjected to genetic modification via Agrobacterium tumefaciens. The duration of high temperature treatment had a significant influence on auxin distribution in isolated and in vitro-cultured microspores and on microspore-derived embryo development. In the “mild” heat-treated (1 day at 32 °C) mcs, auxin localized in a polar way already at the uni-nucleate microspore, which was critical for the initiation of embryos with suspensor-like structure. Assuming a mean mcs radius of 20 μm, endogenous auxin content in a single cell corresponded to concentration of 1.01 μM. In mcs subjected to a prolonged heat (5 days at 32 °C), although auxin concentration increased dozen times, auxin polarization was set up at a few-celled pro-embryos without suspensor. Those embryos were enclosed in the outer wall called the exine. The exine rupture was accompanied by the auxin gradient polarization. Relative quantitative estimation of auxin, using time-lapse imaging, revealed that primordia possess up to 1.3-fold higher amounts than those found in the root apices of transgenic MDEs in the presence of exogenous auxin. Our results show, for the first time, which concentration of endogenous auxin coincides with the first cell division and how the high temperature interplays with auxin, by what affects delay early establishing microspore polarity. Moreover, we present how the local auxin accumulation demonstrates the apical–basal axis formation of the androgenic embryo and directs the axiality of the adult haploid plant. AU - Dubas, Ewa AU - Moravčíková, Jana AU - Libantová, Jana AU - Matušíková, Ildikó AU - Benková, Eva AU - Zur, Iwona AU - Krzewska, Monika ID - 2059 IS - 5 JF - Protoplasma TI - The influence of heat stress on auxin distribution in transgenic B napus microspores and microspore derived embryos VL - 251 ER - TY - JOUR AB - The Balkan Peninsula, characterized by high rates of endemism, is recognised as one of the most diverse and species-rich areas of Europe. However, little is known about the origin of Balkan endemics. The present study addresses the phylogenetic position of the Balkan endemic Ranunculus wettsteinii, as well as its taxonomic status and relationship with the widespread R. parnassiifolius, based on nuclear DNA (internal transcribed spacer, ITS) and plastid regions (rpl32-trnL, rps16-trnQ, trnK-matK and ycf6-psbM). Maximum parsimony and Bayesian inference analyses revealed a well-supported clade formed by accessions of R. wettsteinii. Furthermore, our phylogenetic and network analyses supported previous hypotheses of a likely allopolyploid origin for R. wettsteinii between R. montenegrinus and R. parnassiifolius, with the latter as the maternal parent. AU - Cires Rodriguez, Eduardo AU - Baltisberger, Matthias AU - Cuesta, Candela AU - Vargas, Pablo AU - Prieto, José ID - 2227 IS - 1 JF - Organisms Diversity and Evolution SN - 14396092 TI - Allopolyploid origin of the Balkan endemic Ranunculus wettsteinii (Ranunculaceae) inferred from nuclear and plastid DNA sequences VL - 14 ER - TY - JOUR AB - Plant-specific PIN-formed (PIN) efflux transporters for the plant hormone auxin are required for tissue-specific directional auxin transport and cellular auxin homeostasis. The Arabidopsis PIN protein family has been shown to play important roles in developmental processes such as embryogenesis, organogenesis, vascular tissue differentiation, root meristem patterning and tropic growth. Here we analyzed roles of the less characterised Arabidopsis PIN6 auxin transporter. PIN6 is auxin-inducible and is expressed during multiple auxin-regulated developmental processes. Loss of pin6 function interfered with primary root growth and lateral root development. Misexpression of PIN6 affected auxin transport and interfered with auxin homeostasis in other growth processes such as shoot apical dominance, lateral root primordia development, adventitious root formation, root hair outgrowth and root waving. These changes in auxin-regulated growth correlated with a reduction in total auxin transport as well as with an altered activity of DR5-GUS auxin response reporter. Overall, the data indicate that PIN6 regulates auxin homeostasis during plant development. AU - Cazzonelli, Christopher AU - Vanstraelen, Marleen AU - Simon, Sibu AU - Yin, Kuide AU - Carron Arthur, Ashley AU - Nisar, Nazia AU - Tarle, Gauri AU - Cuttriss, Abby AU - Searle, Iain AU - Benková, Eva AU - Mathesius, Ulrike AU - Masle, Josette AU - Friml, Jirí AU - Pogson, Barry ID - 2472 IS - 7 JF - PLoS One TI - Role of the Arabidopsis PIN6 auxin transporter in auxin homeostasis and auxin-mediated development VL - 8 ER - TY - JOUR AB - As soon as a seed germinates, plant growth relates to gravity to ensure that the root penetrates the soil and the shoot expands aerially. Whereas mechanisms of positive and negative orthogravitropism of primary roots and shoots are relatively well understood [1-3], lateral organs often show more complex growth behavior [4]. Lateral roots (LRs) seemingly suppress positive gravitropic growth and show a defined gravitropic set-point angle (GSA) that allows radial expansion of the root system (plagiotropism) [3, 4]. Despite its eminent importance for root architecture, it so far remains completely unknown how lateral organs partially suppress positive orthogravitropism. Here we show that the phytohormone auxin steers GSA formation and limits positive orthogravitropism in LR. Low and high auxin levels/signaling lead to radial or axial root systems, respectively. At a cellular level, it is the auxin transport-dependent regulation of asymmetric growth in the elongation zone that determines GSA. Our data suggest that strong repression of PIN4/PIN7 and transient PIN3 expression limit auxin redistribution in young LR columella cells. We conclude that PIN activity, by temporally limiting the asymmetric auxin fluxes in the tip of LRs, induces transient, differential growth responses in the elongation zone and, consequently, controls root architecture. AU - Rosquete, Michel AU - Von Wangenheim, Daniel AU - Marhavy, Peter AU - Barbez, Elke AU - Stelzer, Ernst AU - Benková, Eva AU - Maizel, Alexis AU - Kleine Vehn, Jürgen ID - 2844 IS - 9 JF - Current Biology TI - An auxin transport mechanism restricts positive orthogravitropism in lateral roots VL - 23 ER - TY - JOUR AB - Lateral root (LR) formation is initiated when pericycle cells accumulate auxin, thereby acquiring founder cell (FC) status and triggering asymmetric cell divisions, giving rise to a new primordium. How this auxin maximum in pericycle cells builds up and remains focused is not understood. We report that the endodermis plays an active role in the regulation of auxin accumulation and is instructive for FCs to progress during the LR initiation (LRI) phase. We describe the functional importance of a PIN3 (PIN-formed) auxin efflux carrier-dependent hormone reflux pathway between overlaying endodermal and pericycle FCs. Disrupting this reflux pathway causes dramatic defects in the progress of FCs towards the next initiation phase. Our data identify an unexpected regulatory function for the endodermis in LRI as part of the fine-tuning mechanism that appears to act as a check point in LR organogenesis after FCs are specified. AU - Marhavy, Peter AU - Vanstraelen, Marleen AU - De Rybel, Bert AU - Zhaojun, Ding AU - Bennett, Malcolm AU - Beeckman, Tom AU - Benková, Eva ID - 2880 IS - 1 JF - EMBO Journal TI - Auxin reflux between the endodermis and pericycle promotes lateral root initiation VL - 32 ER - TY - JOUR AB - The apical-basal axis of the early plant embryo determines the body plan of the adult organism. To establish a polarized embryonic axis, plants evolved a unique mechanism that involves directional, cell-to-cell transport of the growth regulator auxin. Auxin transport relies on PIN auxin transporters [1], whose polar subcellular localization determines the flow directionality. PIN-mediated auxin transport mediates the spatial and temporal activity of the auxin response machinery [2-7] that contributes to embryo patterning processes, including establishment of the apical (shoot) and basal (root) embryo poles [8]. However, little is known of upstream mechanisms guiding the (re)polarization of auxin fluxes during embryogenesis [9]. Here, we developed a model of plant embryogenesis that correctly generates emergent cell polarities and auxin-mediated sequential initiation of apical-basal axis of plant embryo. The model relies on two precisely localized auxin sources and a feedback between auxin and the polar, subcellular PIN transporter localization. Simulations reproduced PIN polarity and auxin distribution, as well as previously unknown polarization events during early embryogenesis. The spectrum of validated model predictions suggests that our model corresponds to a minimal mechanistic framework for initiation and orientation of the apical-basal axis to guide both embryonic and postembryonic plant development. AU - Wabnik, Krzysztof T AU - Robert, Hélène AU - Smith, Richard AU - Friml, Jirí ID - 527 IS - 24 JF - Current Biology TI - Modeling framework for the establishment of the apical-basal embryonic axis in plants VL - 23 ER - TY - JOUR AB - As sessile organisms, plants have to be able to adapt to a continuously changing environment. Plants that perceive some of these changes as stress signals activate signaling pathways to modulate their development and to enable them to survive. The complex responses to environmental cues are to a large extent mediated by plant hormones that together orchestrate the final plant response. The phytohormone cytokinin is involved in many plant developmental processes. Recently, it has been established that cytokinin plays an important role in stress responses, but does not act alone. Indeed, the hormonal control of plant development and stress adaptation is the outcome of a complex network of multiple synergistic and antagonistic interactions between various hormones. Here, we review the recent findings on the cytokinin function as part of this hormonal network. We focus on the importance of the crosstalk between cytokinin and other hormones, such as abscisic acid, jasmonate, salicylic acid, ethylene, and auxin in the modulation of plant development and stress adaptation. Finally, the impact of the current research in the biotechnological industry will be discussed. AU - O'Brien, José AU - Benková, Eva ID - 827 JF - Frontiers in Plant Science TI - Cytokinin cross talking during biotic and abiotic stress responses VL - 4 ER - TY - JOUR AB - The plant root system is essential for providing anchorage to the soil, supplying minerals and water, and synthesizing metabolites. It is a dynamic organ modulated by external cues such as environmental signals, water and nutrients availability, salinity and others. Lateral roots (LRs) are initiated from the primary root post-embryonically, after which they progress through discrete developmental stages which can be independently controlled, providing a high level of plasticity during root system formation. Within this review, main contributions are presented, from the classical forward genetic screens to the more recent high-throughput approaches, combined with computer model predictions, dissecting how LRs and thereby root system architecture is established and developed. AU - Cuesta, Candela AU - Wabnik, Krzysztof T AU - Benková, Eva ID - 828 JF - Frontiers in Plant Science TI - Systems approaches to study root architecture dynamics VL - 4 ER -