The role of auxin transporters and receptors in adventitious rooting of Arabidopsis thaliana pre-etiolated flooded seedlings

Adventitious roots (ARs) form from above-ground organs, and auxins are major regulators of AR development. TIR1/AFB F-box proteins act as well-established auxin receptors. Auxin transport involves the PINFORMED (PIN) auxin efflux carriers and AUXIN RESISTANT 1/LIKE AUX1 (AUX1/LAX1) influx carriers. To further elucidate the basis of AR development, we investigated the participation of these proteins and phosphorylation of PINs during adventitious rooting in hypocotyls of pre-etiolated flooded Arabidopsis thaliana seedlings. Mutant and GUS localization studies indicated that AFB2 is important in AR development. AUX1 loss-of-function reduced AR numbers, which could not be reversed by exogenous auxin. Single mutations in LAX1, LAX2 and LAX3 had no negative impact on AR development and the first and last mutations even promoted it. Double and triple mutants of AUX1, LAX1, LAX2 and LAX3 significantly reduced rooting, which was reversed by exogenous auxin. AUX1 was essential in AR establishment, with LAX3 apparently acting in conjunction. Proper phosphorylation of PINs by PID, WAG1 and WAG2 and auxin transport direction were equally essential for AR establishment. PIN1, AUX1 and AFB2 (overexpression) and LAX1, LAX3, PIN4 and PIN7 (downregulation) emerged as potential targets for genetic manipulation aiming at improving AR development.Plant science

Comparative adventitious root development in pre-etiolated and flooded Arabidopsis hypocotyls exposed to different auxins

Adventitious roots (ARs) emerge from stems, leaves or hypocotyls, being strategic for clonal propagation. ARs may develop spontaneously, upon environmental stress or hormonal treatment. Auxins strongly influence AR development (ARD), depending on concentration and kind. However, the role of different types of auxin is rarely compared at the molecular level. Rooting triggered by light exposure and flooding was examined in intact etiolated Arabidopsis thaliana hypocotyls treated with distinct auxin types. Morphological aspects, rooting-related gene expression profiles, and IAA immunolocalization were recorded. NAA and 2,4-D effects were highly dose-dependent; at higher concentrations NAA inhibited root growth and 2,4-D promoted callus formation. NAA yielded the highest number of roots, but inhibited elongation. IAA increased the number of roots with less interference in elongation, yielding the best overall rooting response. IAA was localized close to the tissues of root origin. Auxin stimulated ARD was marked by increased expression of PIN1 and GH3.3. NAA treatment induced expression of CYCB1, GH3.6 and ARF8. These NAA-specific responses may be associated with the development of numerous shorter roots. In contrast, expression of the auxin action inhibitor IAA28 was induced by IAA. Increased PIN1 expression indicated the relevance of auxin efflux transport for focusing in target cells, whereas GH3.3 suggested tight control of auxin homeostasis. IAA28 increased expression during IAA-induced ARD differs from what was previously reported for lateral root development, pointing to yet another possible difference in the molecular programs of these two developmental processes.Plant science

Specialized Plant Metabolism Characteristics and Impact on Target Molecule Biotechnological Production.

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI linkPlant secondary metabolism evolved in the context of highly organized and differentiated cells and tissues, featuring massive chemical complexity operating under tight environmental, developmental and genetic control. Biotechnological demand for natural products has been continuously increasing because of their significant value and new applications, mainly as pharmaceuticals. Aseptic production systems of plant secondary metabolites have improved considerably, constituting an attractive tool for increased, stable and large-scale supply of valuable molecules. Surprisingly, to date, only a few examples including taxol, shikonin, berberine and artemisinin have emerged as success cases of commercial production using this strategy. The present review focuses on the main characteristics of plant specialized metabolism and their implications for current strategies used to produce secondary compounds in axenic cultivation systems. The search for consonance between plant secondary metabolism unique features and various in vitro culture systems, including cell, tissue, organ, and engineered cultures, as well as heterologous expression in microbial platforms, is discussed. Data to date strongly suggest that attaining full potential of these biotechnology production strategies requires being able to take advantage of plant specialized metabolism singularities for improved target molecule yields and for bypassing inherent difficulties in its rational manipulation

Allelopathic potential of Psychotria leiocarpa, a dominant understorey species of subtropical forests

AbstractPsychotria leiocarpa is an understorey woody shrub native to the forests of southern Brazil, which occurs in groups of relatively high density. Leaves of field-grown plants contain approximately 2.5% of their dry weight as the N-glycosylated indolic alkaloid N,β-d-glucopyranosyl vincosamide (GPV). To find out if allelopathy could play a role in the distribution pattern of the species, several assays were performed. Aqueous extracts of dried powdered leaves at 4% (w/v) collected during the winter of 2004 inhibited the germination and/or early growth of three different test species. Lactuca sativa plantlets were affected when grown in soil containing dried P. leiocarpa leaves and on plates containing aqueous extracts of leaves of the same species. Partial chemical characterization of the extract was carried out and an allelopathic effect of the purified major leaf alkaloid GPV was not observed at the highest concentration tested of 10 ppm. Experiments with different organic extracts and sequential extractions were also performed. The data suggested that polar phenolic compounds or iridoids are responsible for the phytotoxic effect observed