Systemic signalling through translationally controlled tumour protein controls lateral root formation in Arabidopsis

The plant body plan and primary organs are established during embryogenesis. However, in contrast to animals, plants have the ability to generate new organs throughout their whole life. These give them an extraordinary developmental plasticity to modulate their size and architecture according to environmental constraints and opportunities. How this plasticity is regulated at the whole-organism level is elusive. Here we provide evidence for a role for translationally controlled tumour protein (TCTP) in regulating the iterative formation of lateral roots in Arabidopsis. AtTCTP1 modulates root system architecture through a dual function: as a general constitutive growth promoter enhancing root elongation and as a systemic signalling agent via mobility in the vasculature. AtTCTP1 encodes mRNAs with long-distance mobility between the shoot and roots. Mobile shoot-derived TCTP1 gene products act specifically to enhance the frequency of lateral root initiation and emergence sites along the primary root pericycle, while root elongation is controlled by local constitutive TCTP1 expression and scion size. These findings uncover a novel type for an integrative signal in the control of lateral root initiation and the compromise for roots between branching more profusely or elongating further. They also provide the first evidence in plants of an extracellular function of the vital, highly expressed ubiquitous TCTP1.This work was supported by The Australian National University and a Postgraduate Research Scholarship through the Australian Government Research Training Program

Diel- and temperature-driven variation of leaf dark respiration rates and metabolite levels in rice

Leaf respiration in the dark (R-dark) is often measured at a single time during the day, with hot-acclimation lowering R-dark at a common measuring temperature. However, it is unclear whether the diel cycle influences the extent of thermal acclimation of R-dark, or how temperature and time of day interact to influence respiratory metabolites. To examine these issues, we grew rice under 25 degrees C : 20 degrees C, 30 degrees C : 25 degrees C and 40 degrees C : 35 degrees C day : night cycles, measuring R-dark and changes in metabolites at five time points spanning a single 24-h period. R-dark differed among the treatments and with time of day. However, there was no significant interaction between time and growth temperature, indicating that the diel cycle does not alter thermal acclimation of R-dark. Amino acids were highly responsive to the diel cycle and growth temperature, and many were negatively correlated with carbohydrates and with organic acids of the tricarboxylic acid (TCA) cycle. Organic TCA intermediates were significantly altered by the diel cycle irrespective of growth temperature, which we attributed to light-dependent regulatory control of TCA enzyme activities. Collectively, our study shows that environmental disruption of the balance between respiratory substrate supply and demand is corrected for by shifts in TCA-dependent metabolites.Peer reviewe

Molecular and physiological responses during thermal acclimation of leaf photosynthesis and respiration in rice

To further our understanding of how sustained changes in temperature affect the carbon economy of rice (Oryza sativa), hydroponically grown plants of the IR64 cultivar were developed at 30°C/25°C (day/night) before being shifted to 25/20°C or 40/35°C. Leaf messenger RNA and protein abundance, sugar and starch concentrations, and gas‐exchange and elongation rates were measured on preexisting leaves (PE) already developed at 30/25°C or leaves newly developed (ND) subsequent to temperature transfer. Following a shift in growth temperature, there was a transient adjustment in metabolic gene transcript abundance of PE leaves before homoeostasis was reached within 24 hr, aligning with Rdark (leaf dark respiratory CO2 release) and An (net CO2 assimilation) changes. With longer exposure, the central respiratory protein cytochrome c oxidase (COX) declined in abundance at 40/35°C. In contrast to Rdark, An was maintained across the three growth temperatures in ND leaves. Soluble sugars did not differ significantly with growth temperature, and growth was fastest with extended exposure at 40/35°C. The results highlight that acclimation of photosynthesis and respiration is asynchronous in rice, with heat‐acclimated plants exhibiting a striking ability to maintain net carbon gain and growth when exposed to heat‐wave temperatures, even while reducing investment in energy‐conserving respiratory pathways.Peer reviewe

Role of the Arabidopsis PIN6 auxin transporter in auxin homeostasis and auxin-mediated development

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.Christopher I. Cazzonelli, Marleen Vanstraelen, Sibu Simon, Kuide Yin, Ashley Carron-Arthur, Nazia Nisar, Gauri Tarle, Abby J. Cuttriss¤, Iain R. Searle, Eva Benkova, Ulrike Mathesius, Josette Masle, Jiří Friml, Barry J. Pogso

The effects of elevated CO2 concentrations on cell division rates, growth patterns, and blade anatomy in young wheat plants are modulated by factors related to leaf position, vernalization, and genotype.

This study demonstrates that elevated [CO2] has profound effects on cell division and expansion in developing wheat (Triticum aestivum L.) leaves and on the quantitative integration of these processes in whole-leaf growth kinetics, anatomy, and carbon content. The expression of these effects, however, is modified by intrinsic factors related to genetic makeup and leaf position, and also by exposure to low vernalizing temperatures at germination. Beyond these interactions, leaf developmental responses to elevated [CO2] in wheat share several remarkable features that were conserved across all leaves examined. Most significantly: (a) the contribution of [CO2] effects on meristem size and activity in driving differences in whole-blade growth kinetics and final dimensions; (b) an anisotropy in cellular growth responses to elevated [CO2], with final cell length and expansion in the paradermal plane being highly conserved, even when the rates and duration of cell elongation were modified, while cell cross-sectional areas were increased; (c) tissue-specific effects of elevated [CO2], with significant modifications of mesophyll anatomy, including an increased extension of intercellular air spaces and the formation of, on average, one extra cell layer, while epidermal anatomy was mostly unaltered. Our results indicate complex developmental regulations of sugar effects in expanding leaves that are subjected to genetic variation and influenced by environmental cues important in the promotion of floral initiation. They also provide insights into apparently contradictory and inconsistent conclusions of published CO2 enrichment studies in wheat

Elaboration du nombre d'épis d'un peuplement de blé d'hiver en situation de compétition pour l'azote II. Modélisation du nombre d'épis

Nous proposons un modèle de prévision du nombre d'épis formés par un peuplement de blé d'hiver en situation de compétition pour l'azote seul pendant le cycle. Ce modèle repose sur : - la transposition au champ de l'existence, pour toute talle, d'un stade critique à 3 feuilles, montrée en pots (Masle-Meynard, 1981) : nous supposons que seules les talles ayant au moins 3 feuilles au début de la compétition montent ; - la connaissance des lois régissant le processus de tallage : - le rang de la dernière talle apparue sur un pied permet de dater par rapport au stade foliaire de son brin-maître le moment auquel il a commencé à manquer d'azote ; - le modèle d'apparition des feuilles et talles successives d'un pied permet de reconstituer à cette date la séquence de tallage du pied considéré (nombre et nature des talles, leur nombre de feuilles). La prévision à laquelle nous aboutissons est testée 3 années successives, pour une même variété, en Champagne crayeuse. Elle se révèle, dans la plupart des cas, satisfaisante. Les cas d'erreur suggèrent un déplacement du stade critique observé en pots, selon la date de semis et le type de sol (régime thermique en particulier), 2 facteurs susceptibles de modifier la relation croissance racinaire-stade foliaire

Relations entre croissance et développement pendant la montaison d'un peuplement de blé d'hiver. Influence des conditions de nutrition

Nous étudions au champ l'influence des conditions de nutrition (compétition pour l'azote ou la lumière) sur l'évolution d'un peuplement de blé d'hiver pendant la montaison, en nous attachant plus particulièrement à l'analyse du phénomène de régression de talles. Il apparaît que les conditions d'alimentation n'affectent pas de manière sensible, dans les gammes explorées, le déroulement du développement : celui-ci constitue une trame très stable dans une région donnée, fixée par les facteurs climatiques. Elles interviennent par contre de manière très importante sur la croissance ; l'apparition d'une compétition pour l'azote ou la lumière provoque un ralentissement de la croissance de toutes les talles, mais variable selon leur âge. On constate que le facteur limitant est surtout utilisé pour la croissance des talles les plus âgées du peuplement. Lorsqu'on passe à des talles de plus en plus jeunes, la vitesse de croissance est de plus en plus faible, voire s'annule : il s'agit alors de cas de régression. La régression apparaît comme un phénomène d'origine principalement nutritionnelle ; sa précocité, son ampleur ne peuvent être mises en relation avec aucun stade de développement précis, mais se révèlent directement liées à la date d'apparition de la compétition dans le cycle de la culture. Nous analy

Elaboration du nombre d'épis d'un peuplement de blé d'hiver en situation de compétition pour l'azote II. Modélisation du nombre d'épis

Nous proposons un modèle de prévision du nombre d'épis formés par un peuplement de blé d'hiver en situation de compétition pour l'azote seul pendant le cycle. Ce modèle repose sur : - la transposition au champ de l'existence, pour toute talle, d'un stade critique à 3 feuilles, montrée en pots (Masle-Meynard, 1981) : nous supposons que seules les talles ayant au moins 3 feuilles au début de la compétition montent ; - la connaissance des lois régissant le processus de tallage : - le rang de la dernière talle apparue sur un pied permet de dater par rapport au stade foliaire de son brin-maître le moment auquel il a commencé à manquer d'azote ; - le modèle d'apparition des feuilles et talles successives d'un pied permet de reconstituer à cette date la séquence de tallage du pied considéré (nombre et nature des talles, leur nombre de feuilles). La prévision à laquelle nous aboutissons est testée 3 années successives, pour une même variété, en Champagne crayeuse. Elle se révèle, dans la plupart des cas, satisfaisante. Les cas d'erreur suggèrent un déplacement du stade critique observé en pots, selon la date de semis et le type de sol (régime thermique en particulier), 2 facteurs susceptibles de modifier la relation croissance racinaire-stade foliaire