Proceedings of international symposia on abscission processes in horticulture and non-destructive assessment of fruit attributes

International Horticultural Congress on Horticulture : Sustaining Lives, Livelihoods and Landscapes : International Symposia on Abscission Processes in Horticulture and Non-Destructive Assessment of Fruit Attributes, Brisbane, AUS, 17-/08/2014 - 22/08/201

Plant Organ Abscission: From Models to Crops

Plant organ abscission is a developmental process regulated by the environment, stress, pathogens and the physiological status of the plant. In particular, seed and fruit abscission play an important role in seed dispersion and plant reproductive success and are common domestication traits with important agronomic consequences for many crop species. Indeed, in natural populations, shedding of the seed or fruit at the correct time is essential for reproductive success, while for crop species the premature or lack of abscission may be either beneficial or detrimental to crop productivity. The use of model plants, in particular Arabidopsis and tomato, have led to major advances in our understanding of the molecular and cellular mechanisms underlying organ abscission, and now many workers pursue the translation of these advances to crop species. Organ abscission involves specialized cell layers called the abscission zone (AZ), where abscission signals are perceived and cell separation takes place for the organ to be shed. A general model for plant organ abscission includes (1) the differentiation of the AZ, (2) the acquisition of AZ cells to become competent to respond to various abscission signals, (3) response to signals and the activation of the molecular and cellular processes that lead to cell separation in the AZ and (4) the post-abscission events related to protection of exposed cells after the organ has been shed. While this simple four-phase framework is helpful to describe the abscission process, the exact mechanisms of each stage, the differences between organ types and amongst diverse species, and in response to different abscission inducing signals are far from elucidated. For an organ to be shed, AZ cells must transduce a multitude of both endogenous and exogenous signals that lead to transcriptional and cellular and ultimately cell wall modifications necessary for adjacent cells to separate. How these key processes have been adapted during evolution to allow for organ abscission to take place in different locations and under different conditions is unknown. The aim of the current collection of articles is to present and be able to compare recent results on our understanding of organ abscission from model and crop species, and to provide a basis to understand both the evolution of abscission in plants and the translation of advances with model plants for applications in crop species

Nitrate-dependent control of root architecture and N nutrition are altered by a plant growth-promoting Phyllobacterium sp

Present Adress: Larcher, M. Observatoire Océanologique de Banyuls, UMR 7621, BP 44 66651 Banyuls sur Mer Cedex France Tranbarger, T.J. Centre de Recherche CIRAD, IRD de Montpellier, Laboratoire GeneTrop, BP 5045 34032 Montpellier, FranceInternational audienceBoth root architecture and plant N nutrition are altered by inoculation with the plant growth-promoting rhizobacteria (PGPR) Phyllobacterium strain STM196. It is known that NO3- and N metabolites can act as regulatory signals on root development and N transporters. In this study, we investigate the possible interrelated effects on root development and N transport. We show that the inhibition of Arabidopsis lateral root growth by high external NO3- is overridden by Phyllobacterium inoculation. However, the leaf NO3- pool remained unchanged in inoculated plants. By contrast, the Gln root pool was reduced in inoculated plants. Unexpectedly, NO3- influx and the expression levels of AtNRT1.1 and AtNRT2.1 genes coding for root NO(3)(-)transporters were also decreased after 8 days of Phyllobacterium inoculation. Although the mechanisms by which PGPR exert their positive effects remain unknown, our data show that they can optimize plant development independently from N supply, thus alleviating the regulatory mechanisms that operate in axenic conditions. In addition, we found that Phyllobacterium sp. elicited a very strong induction of AtNRT2.5 and AtNRT2.6, both genes preferentially expressed in the shoots whose functions are unknow

Environmental and trophic determinism of fruit abscission and outlook with climate change in tropical regions

International audienceFruit abscission facilitates the optimal conditions and timing of seed dispersal. Environmental regulation of tropical fruit abscission has received little attention, even though climate change may have its strongest impacts in tropical regions. In this study, oil palm fruit abscission was monitored during multiple years in the Benin Republic to take advantage of the climatic seasonality and the continuous fruit production by this species. An innovative multivariable statistical method was used to identify the best predictors of fruit abscission among a set of climate and ecophysiological variables, and the stage of inflorescence and fruit bunch development when the variables are perceived. The effects of climate scenarios on fruit abscission were then predicted based on the calibrated model. We found complex regulation takes place at specific stages of inflorescence and bunch development, even long before the fruit abscission zone is competent to execute abscission. Among the predictors selected, temperature variations during inflorescence and fruit bunch development are major determinants of the fruit abscission process. Furthermore, the timing of ripe fruit drop is determined by temperature in combination with the trophic status. Finally, climate simulations revealed that the abscission process is robust and is more affected by seasonal variations than by extreme scenarios. Our investigations highlighted the central function of the abscission zone as the sensor of environmental signals during reproductive development. Coupling ecophysiological and statistical modeling was an efficient approach to disentangle this complex environmental regulation. K E Y W O R D S climate change, Elaeis guineensis, environmental regulation, fruit abscission, multivariable model

EPIP as an abscission promoting agent in the phytohormonal pathway

Understanding the mechanisms underlying the activation of the abscission zone (AZ) responsible for organ separation from plant body in crop species will help improve their yielding and economic importance. Special attention has been given recently to the role of the INFLORESCENCE DEFICIENT IN ABSCISSION protein, particularly its functional fragment, EPIP peptide. Its stimulatory effect on abscission in different crops has been demonstrated. Recently we described the role of EPIP in the redox, lipid, and pectin-related events taking place in AZ of Lupinus luteus flowers, which undergo massive abscission in natural conditions. To further examine EPIP contribution in AZ functioning, here, we analyze its impact on the ultrastructural changes, synthesis of two hormonal abscission stimulators - abscisic acid (ABA) and ethylene (ET), and the appearance of phosphoproteins. As our results show, the response of flower AZ to exogenous EPIP involves the induction of distinct modifications related to the one hand with upregulation of cell activity but on the other hand degradation processes and possible autophagy. Furthermore, the EPIP stimulated biosynthesis pathways of ABA and ET precisely in AZ cells. In addition, progressive phosphorylation of proteins has been observed under EPIP influence. The highly accumulated ones were identified as those, related to primary metabolism and reactive oxygen species homeostasis, and their role in abscission has been discussed. To summarizing, the presented detailed description of EPIP action in AZ cells in combination with our previous data offers new insights into its regulatory function and provides opportunities to counteract excessive flower abscission in lupine

A macro-array-based screening approach to identify transcriptional factors involved in the nitrogen-related root plasticity response of Arabidopsis thaliana

We examined changes in the root architecture and morphology of Arabidopsis thaliana grown on vertically-oriented agar plates containing 0.1, 0.5 or 10 mM KNO$_3$, or 0.5 mM KNO$_3$ supplemented with 5 mM glutamine or asparagine. The roots of 14-day-old plants grown with 10 mM KNO$_3$ had the least number and length of lateral roots (LR) in contrast to plants grown on the other nitrogen sources. NO$_3^-$ inhibited LR development at a stage after the initiation of primordia and before emergence of the LR. To identify the regulatory genes involved in the root response, we constructed a macro-array that contained 126 putative transcriptional factor ESTs to analyze their expression profiles. Expression patterns in roots or shoots of plants grown on different N sources indicated that only a limited number of genes responded. The highest level of variation in expression was obtained when comparing the roots of plants supplied with 10 mM versus 0.5 mM NO$_3^-$.Utilisation de macro-arrays pour identifier des facteurs de transcription impliqués dans la réponse de plasticité racinaire à l'azote chez Arabidopsis thaliana. Des plantes d'Arabidopsis thaliana sont cultivées dans des boîtes de Pétri verticales, sur un milieu gélosé où l'azote est apporté sous forme de KNO$_3$ 0,1, 0,5 ou 10 mM, ou de KNO$_3$ 0,5 mM additionné de glutamine ou d'asparagine 5 mM. Le traitement KNO$_3$ 10 mM correspond aux plus faibles nombre et longueur de racines latérales. Leur développement est inhibé à un stade postérieur à l'initiation des primordia et antérieur à leur émergence. Des membranes Nylon (macro-arrays) contenant 126 EST de facteurs de transcription potentiels sont construites afin d'identifier des gènes régulateurs impliqués dans cette réponse d'architecture racinaire. L'analyse des profils d'expression dans les racines et les parties aériennes de plantes cultivées sur les différentes sources d'azote indiquent que les gènes répondant aux traitements sont peu nombreux, et que la plus forte variation est obtenue lorsque l'on compare les traitements KNO$_3$ 10 mM et KNO$_3$ 0,5 mM

A phenotypic test for delay of abscission and non-abscission oil palm fruit and validation by abscission marker gene expression analysis

International Horticultural Congress on Horticulture : Sustaining Lives, Livelihoods and Landscapes : International Symposia on Abscission Processes in Horticulture and Non-Destructive Assessment of Fruit Attributes, Brisbane, AUS, 17-/08/2014 - 22/08/2014Knowledge of the cell separation processes underlying organ abscission is limited mainly to the eudicot model systems tomato and Arabidopsis, while less is known about the mechanisms in crop species in general, and monocots in particular. Here we describe a simple phenotypic screen for oil palm plant lines with delayed or non-abscising fruit. The phenotypic test was used on the two species of oil palm including Elaeis guineensis and E. oleifera, in addition to their interspecific hybrids, and hybrids backcrossed to E. guineensis. A large variation in abscission phenotypes was observed. Histological analysis revealed similarities and differences in the abscission zone (AZ) of E. guineensis and E. oleifera, and dominant traits were observed in the AZ of the interspecific crosses. The expression of abscission marker genes for a polygalacturonase (EgPG4) and an ethylene synthesis ACO synthase (EgACO) were monitored during abscission of a randomly selected set of plants and in a non-abscising individual identified by the phenotypic test

Proceedings of international symposia on abscission processes in horticulture and non-destructive assessment of fruit attributes

Knowledge of the cell separation processes underlying organ abscission is limited mainly to the eudicot model systems tomato and Arabidopsis, while less is known about the mechanisms in crop species in general, and monocots in particular. Here we describe a simple phenotypic screen for oil palm plant lines with delayed or non-abscising fruit. The phenotypic test was used on the two species of oil palm including Elaeis guineensis and E. oleifera, in addition to their interspecific hybrids, and hybrids backcrossed to E. guineensis. A large variation in abscission phenotypes was observed. Histological analysis revealed similarities and differences in the abscission zone (AZ) of E. guineensis and E. oleifera, and dominant traits were observed in the AZ of the interspecific crosses. The expression of abscission marker genes for a polygalacturonase (EgPG4) and an ethylene synthesis ACO synthase (EgACO) were monitored during abscission of a randomly selected set of plants and in a non-abscising individual identified by the phenotypic test