Browsing by Subject "Lupinus albus"

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Functional characterization of genes involved in development and function of cluster root in Lupinus albus
(2020) Zhou, Yaping; Ludewig, Uwe
White lupin cluster roots are specialized brush-like root structures that are formed in some species under phosphorus (P)-deficient conditions. They intensely secrete protons and organic anions for solubilization and acquisition of sparingly soluble phosphates. Because of the outstanding P efficiency of white lupin, this species has served as an illuminating model for plant adaptations to phosphorus deficiency. Since decades, numerous studies were carried out to gain a comprehensive knowledge of cluster root formation and function. The aim of this study was to identify genetic components involved in cluster root development and to identify the transporter genes that are potentially involved in citrate andmalate secretion under P deficiency as well as under toxic aluminium (Al) exposure.
Molecular regulation of components of root development and nutrient uptake in white lupin (Lupinus albus L.)
(2023) Olt, Philipp; Ludewig, Uwe
White lupin (Lupinus albus L.) is specially adapted to sites with low availability of plant-available phosphorus (P), which is of particular agricultural importance because of chemical P fixation in the soil and limited reserves of P fertilizer resources. With special root structures, the cluster roots (syn. proteoid roots), it considerably increases the root surface area and excretes root exudates such as anions of organic acids, which make it possible to release phosphate ions from poorly soluble phosphate compounds in the soil and make them available to plants. The characteristic structure of these cluster roots usually consists of a lateral root with certain sections that have a significantly higher density of further lateral roots (rootlets) than the rest of the lateral root. In addition, the rootlets are evenly limited in length and, as they grow bundled in the cluster sections, the structure of cluster roots is reminiscent of a bottle brush. Cluster roots are also formed by other plant species such as some species from the Proteaceae family, but in contrast to these slow- growing and perennial woody plants, white lupin with its short life cycle and small size is an ideal model organism for the study of these special root structures. In addition to the mechanisms involved in the function of cluster roots, the regulation of formation and development of cluster roots is also of great importance for basic research in this field. Three studies were carried out as part of this thesis to examine these aspects in more detail. In order to better understand the functional mechanisms involved in the excretion of exudates, the hypothesis that the METAL AND TOXIN EXTRUSION (MATE) transport proteins LaMATE and LaMATE3 transport citrate was tested in the first study. The similarity of the gene sequences of these white lupin proteins with proteins from the MATE/DTX family, of which citrate transport is already known, as well as the increased gene expression of LaMATE and LaMATE3 in mature cluster roots led to this assumption. However, electrophysiological studies of the proteins with 13C- labeled citrate showed that LaMATE and LaMATE3 probably do not transport citrate and also the analysis of root exudates from transient loss-of-function mutants could not confirm the involvement of LaMATE in the transport of citrate. However, the excretion of the isoflavonoid genistein was found to be significantly reduced in the transient loss-of-function mutants, leading to the hypothesis that LaMATE may be involved in the exudation of isoflavonoids in mature cluster roots. As a result of the mobilization of phosphates through the excretion of organic acids, other cations such as manganese (Mn) also dissolve, which leads to increased Mn concentrations in the soil solution. As manganese uptake in the roots is not actively regulated, Mn accumulates in the plant, which has a toxic effect in higher concentrations. For this reason, white lupin needs a strategy to counteract toxic manganese accumulation, which was investigated in more detail in the second study. The observation that a greater increase in Mn concentration could be measured in the leaves than in the roots after elevated Mn exposure of white lupin indicates an actively regulated transport of excess Mn in the plant. The METAL TOLERANCE PROTEIN (MTP) AtMTP8 is involved in the detoxification of excess Mn in Arabidopsis and the increased gene expression of the corresponding white lupin homolog LaMTP8.1 in plants exposed to elevated Mn concentration suggested that LaMTP8.1 also fulfills a detoxification function. In further experiments, the ability of the LaMTP8.1 protein to transport Mn was demonstrated by heterologous expression of LaMTP8.1 in yeast cells. Furthermore, the high Mn concentrations in the leaves already indicated that the sink of Mn sequestration is located there and since AtMTP8 transports Mn into the vacuole, it was assumed that LaMTP8.1 could be localized in the tonoplast of the leaf cells to transport excess Mn into the vacuoles. This hypothesis was confirmed by homologous expression of LaMTP8.1 combined with a fluorescent marker in white lupin protoplasts. In summary, this study demonstrated that LaMTP8.1 is a vacuolar Mn transporter that mediates the transport of Mn into the vacuoles of leaf cells to detoxify excess Mn. While the first two studies addressed functional and physiological aspects of cluster roots, the third study focused on the mechanisms of formation and development of these root structures. To this end, the main focus was on the CLAVATA3/ EMBRYO SURROUNDING REGION (ESR)- RELATED (CLE) peptide family, of which some members regulate root growth in other plant species and enable more precise control of regulation compared to the known growth regulators auxin and cytokinin. In a comprehensive analysis, 30 known and further 25 new, putative CLE peptides were identified in Lupinus albus. Several of the CLE peptides were tested in a hydroponic system on young white lupins for their effects on root development and cluster root formation. The two CLE peptides LaCLE35 (RGVHyPSGANPLHN) and LaCLE55 (RRVHyPSCHyPDPLHN) showed striking inhibitory effects and altered both root growth and cluster root development in an inhibitory manner. The peptide LaCLE35 stood out in particular because it was the only CLE peptide detected in white lupin xylem sap and was therefore investigated in more detail. It was shown that LaCLE35 influences both the density and the length of cluster rootlets, and thus has an effect on the two crucial factors of cluster root formation. The inhibitory effect of CLE35 could be attributed to a suppression of cell elongation and further experiments with split-root setups showed that the externally added synthetic peptide LaCLE35 has a local but not a systemic effect. The investigations of the LaMATE transport proteins and LaMTP8.1-mediated Mn detoxification as well as the overview of the detected CLE peptides in white lupin and the analysis of the inhibitory influences of LaCLE35 on cluster roots form the basis of this thesis and aim to contribute to the understanding of the function, effects and formation of these special root structures.