The influence of abscisic acid on the ethylene biosynthesis pathway in the functioning of the flower abscission zone in Lupinus luteus.

Flower abscission is a highly regulated developmental process activated in response to exogenous (e.g. changing environmental conditions) and endogenous stimuli (e.g. phytohormones). Ethylene (ET) and abscisic acid (ABA) are very effective stimulators of flower abortion in Lupinus luteus, which is a widely cultivated species in Poland, Australia and Mediterranean countries. In this paper, we show that artificial activation of abscission by flower removal caused an accumulation of ABA in the abscission zone (AZ). Moreover, the blocking of that phytohormone's biosynthesis by NDGA (nordihydroguaiaretic acid) decreased the number of abscised flowers. However, the application of NBD - an inhibitor of ET action - reversed the stimulatory effect of ABA on flower abscission, indicating that ABA itself is not sufficient to turn on the organ separation. Our analysis revealed that exogenous ABA significantly accelerated the transcriptional activity of the ET biosynthesis genes ACC synthase (LlACS) and oxidase (LlACO), and moreover, strongly increased the level of 1-aminocyclopropane-1-carboxylic acid (ACC) - ET precursor, which was specifically localized within AZ cells. We cannot exclude the possibility that ABA mediates flower abscission processes by enhancing the ET biosynthesis rate. The findings of our study will contribute to the overall basic knowledge on the phytohormone-regulated generative organs abscission in L. luteus.

Molecular cloning of the BLADE-ON-PETIOLE gene and expression analyses during nodule development in Lupinus luteus.

The BLADE-ON-PETIOLE (BOP) genes have been recently shown to play an essential role in many physiological processes, including embryogenesis, meristem determinacy, leaf patterning and nodule development. In our research we used Lupinus luteus, a plant with great agronomic potential due to its high protein content and nitrogen fixation ability. In this work, LlBOP in L. luteus was identified for the first time and its expression during nodule development was analyzed. The high expression levels of LlBOP and LlLbI (LEGHEMOGLOBIN), essential to nitrogen-fixing symbiosis, were noted in the developing root nodules and were correlated with the occurrence of leghemoglobin. All of these data indicate that LlBOP is an important regulator of root nodule formation and functioning in L. luteus.

The involvement of InMIR167 in the regulation of expression of its target gene InARF8, and their participation in the vegetative and generative development of Ipomoea nil plants.

The plant hormone auxin plays a critical role in regulating plant growth and development. Recent advances have been made that having improved our understanding of auxin response pathways, primarily by characterizing the genes encoding auxin response factors (ARFs) in Arabidopsis. In addition, the expression of some ARFs is regulated by microRNAs (miRNAs). In Arabidopsis thaliana, ARF6 and ARF8 are targeted by miR167, whereas ARF10, ARF16 and ARF17 are targeted by miR160. Nevertheless, little is known about any possible interactions between miRNAs and the auxin signaling pathway during plant development. In this study, we isolated the miR167 target gene InARF8 cDNA from the cotyledons of the short day plant (SDP) Ipomoea nil (named also Pharbitis nil). Additionally, the In-miR167 precursor was identified from the I. nil EST database and analyses of InARF8 mRNA, In-pre-miR167 and mature miR167 accumulation in the plant's vegetative and generative organs were performed. The identified cDNA of InARF8 contains a miR167 complementary sequence and shows significant similarity to ARF8 cDNAs of other plant species. The predicted amino acid sequence of InARF8 includes all of the characteristic domains for ARF family transcription factors (B3 DNA-binding domain, AUX/IAA-CTD and a glutamine-rich region). Quantitative RT-PCR reactions and in situ hybridization indicated that InARF8 was expressed primarily in the shoot apices, leaf primordia and hypocotyls of I. nil seedlings, as well as in flower pistils and petals. The InARF8 transcript level increased consistently during the entire period of pistil development, whereas in the stamens, the greatest transcriptional activity occurred only during the intensive elongation phase. Additionally, an expression analysis of both the precursor In-pre-miR167 molecules identified and mature miRNA was performed. We observed that, in most of the organs examined, the InARF8 expression pattern was opposite to that of MIR167, indicating that the gene's activity was regulated by mRNA cleavage. Our findings suggested that InARF8 and InMIR167 participated in the development of young tissues, especially the shoot apices and flower elements. The main function of MIR167 appears to be to regulate InARF8 organ localization.

[Abscisic acid metabolism]. / Metabolizm kwasu abscysynowego.

Abscisic acid is one of the plant hormones that determines normal growth and development, i.e. seeds ripening and germination, stomata opening and closure, flowering and stress responses. An appropriate level of endogenous ABA plays a key role in the regulation of most of these processes. Its content in a particular tissue is a balance between the rate of its biosynthesis, oxidative degradation and formation of inactive derivatives (mainly ester). The progress on ABA metabolism was relatively slow in the past. Application of modern molecular biology methods let the most of genes encoding enzymes involved in the regulation of ABA metabolism be identified and contributed to the understanding of its action.

[Jasmonate biosynthesis--the latest discoveries]. / Biosynteza jasmonianów u roslin--najnowsze odkrycia.

Jasmonates are plant hormones involved in many growth and development processes. They also participate in plant defense responses. Current progress in the study on biosynthesis and signaling of jasmonates has contributed to the understanding of the mechanisms regulating concentration of these hormones in the cell. Sustaining a proper level of jasmonates allow the plant to respond appropriately to changing conditions. It is possible due to the large number of enzymes and genes involved in biosynthesis of these hormones as well as multilevel control of their expression.

[Jasmonate signaling pathway--new insight]. / Szlak sygnalowy kwasu jasmonowego--nowe informacje.

Significant progress which was made during last few years in research of jasmonic acid signaling pathway yielded surprising information about chemical form of a signaling molecule of the hormone, which turned out to be its conjugate with amino acid isoleucine. Function of jasmonic acid receptor is more and more frequently attributed to COI1 protein which is structurally and functionally similar to the auxin receptor TIR1. Signal perception takes place in the nucleus and leads to the activation of SCF(COI1) ubiquitine ligase and consequently to proteolysis of transcription repressors, the JAZ proteins. Reduced pool of these negative regulators enables to activate the transcription factors (i. e. ERF1, WRKY70, MYC2), as well as expression of genes involved in defense responses of plants (i. e. PDF1.2, VSP1, CHI-B). Jasmonic acid signal transduction pathway, is also subjected to complicated regulations, including both positive, and negative feedbacks, which enable plants react adequately to variable environmental conditions.

Light- and IAA-regulated ACC synthase gene (PnACS) from Pharbitis nil and its possible role in IAA-mediated flower inhibition.

The light- and indole-3-acetic acid (IAA)-regulated 1-aminocyclopropane-1-carboxylic acid (ACC) synthase gene (PnACS) from Pharbitis nil was isolated. Here, it was shown that the gene was expressed in cotyledons, petioles, hypocotyls, root and shoot apexes both in light- and dark-grown seedlings. The highest expression level of PnACS was found in the roots. IAA applied to the cotyledons of P. nil seedlings caused a clear increase of PnACS messenger accumulation in all the organs examined. In this case, the most IAA-responsive were the hypocotyls. Our studies revealed that the PnACS transcript level in the cotyledons exhibited diurnal oscillations under both long-day (LD) and short-day (SD) conditions. IAA applied at the beginning of inductive darkness caused a dramatic increase in the expression of PnACS, suggesting that the inhibitory effect of IAA on P. nil flowering may result from its stimulatory effect on ethylene production.

[Ethylene signal transduction pathway]. / Szlaki przekazywania sygnalów indukowane przez etylen.

Ethylene is involved in the regulation of many growth and developmental processes in plants. Signaling pathways of the hormone are activated by five receptors, which are localized in membranes of endoplasmic reticulum and are similar to bacterial two-component histidine kinases. In the air, ethylene receptors activate CTR1 protein, which is a negative regulator (repressor) of nuclear protein--EIN2. In turn, EIN2 is an activator of transcriptional factors cascade responsible for the regulation of the expression of ethylene response genes. The level of EIN3, as well as other elements of ethylene signal transduction pathway, is subjected to complicated regulations on transcriptional and posttranslational levels, in which other internal and environmental factors are involved.

[Regulation of ethylene biosynthesis in plants]. / Regulacja biosyntezy etylenu u roslin.

Ethylene is one of the plant hormones that controls growth and development. There are many responses regulated via ethylene in response to exogenous stimuli. Research on ethylene biosynthesis and the signalling pathway enabled us to understand the mechanism of the regulation of these responses. Different temporal and spatial expression of genes encoding enzymes involved in ethylene biosynthesis is of great importance for the regulation of ethylene responses. Also, post-translational regulation of the enzymes seems to be a key regulatory mechanism for the control of their activity. Because of versatile regulation of its production, ethylene can control plant development at many levels.