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Populus metacaspases - The function of two type II metacaspases in woody tissues of Populus trees

ABSTRACT: Metacaspases (MCs) are cysteine proteases that are implicated in programmed cell death of plants. AtMC9 (Arabidopsis thaliana Metacaspase9) is a member of the Arabidopsis MC family that controls the rapid autolysis of the xylem vessel elements, but its downstream targets in the xylem remain uncharacterized. PttMC13 and PttMC14 were identified as AtMC9 homologs of hybrid aspen (Populus tremula x tremuloides). A proteomic analysis was conducted in xylem tissues of transgenic hybrid aspen trees which carried either an overexpression or an RNAi construct for PttMC13 and PttMC14. The proteomic analysis revealed modulation of levels of both previously known targets of metacaspases, such as Tudor staphylococcal nuclease, heat shock proteins and 14-3-3 proteins as well as novel targets, such as homologs of the PUTATIVE ASPARTIC PROTEASE 3 (PASPA3) (PASPA) and the cysteine protease RD21 by PttMC13 and PttMC14. We identified here the pathways and processes that are modulated by PttMC13 and PttMC14 in xylem tissues. In particular, the results indicate involvement of PttMC13 and/or PttMC14 in controlling not only xylem cell autolysis but also cell death. This work provides a valuable reference dataset on xylem specific metacaspase functions for future functional and biochemical analyses.

INSTRUMENT(S): Synapt G2 HDMS

ORGANISM(S): Populus Tremula X Populus Tremuloides

TISSUE(S): Xylem

SUBMITTER: Joakim Bygdell

LAB HEAD: Hannele Tuominen

PROVIDER: PXD007958 | Pride | 2018-01-02

REPOSITORIES: Pride

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Project description:Background Ionic aluminum (mainly Al3+) is rhizotoxic and can be present in acid soils at concentrations high enough to inhibit root growth. Many forest tree species grow naturally in acid soils and often tolerate high concentrations of Al. Previously, we have shown that aspen (Populus tremula) releases citrate and oxalate from roots in response to Al exposure. To obtain further insights into the root responses of aspen to Al, we investigated root gene expression at Al conditions that inhibit root growth. Results Treatment of the aspen roots with 500 µM Al induced a strong inhibition of root growth within 6 h of exposure time. The root growth subsequently recovered, reaching growth rates comparable to that of control plants. Changes in gene expression were determined after 6 h, 2 d, and 10 d of Al exposure. Replicated transcriptome analyses using the Affymetrix poplar genome array revealed a total of 175 significantly up-regulated and 69 down-regulated genes, of which 70% could be annotated based on Arabidopsis genome resources. Between 6 h and 2 d, the number of responsive genes strongly decreased from 202 to 26, and then the number of changes remained low. The responses after 6 h were characterized by genes involved in cell wall modification, ion transport, and oxidative stress. Two genes with prolonged induction were closely related to the Arabidopsis Al tolerance genes ALS3 (for Al sensitive 3) and MATE (for multidrug and toxin efflux protein, mediating citrate efflux). Patterns of expression in different plant organs and in response to Al indicated that the two aspen genes are homologs of the Arabidopsis ALS3 and MATE. Conclusion Exposure of aspen roots to Al results in a rapid inhibition of root growth and a large change in root gene expression. The subsequent root growth recovery and the concomitant reduction in the number of responsive genes presumably reflect the success of the roots in activating Al tolerance mechanisms. The aspen genes ALS3 and MATE may be important components of these mechanisms.

Project description:Background: Solubilized aluminum (Al) is rhizotoxic and can be present in acid soils at levels that inhibit root growth. Acid soils are found throughout the world and often support forests. However, unlike in herbaceous plants, little is known about the mechanisms by which forest trees respond to and tolerate Al. To begin to elucidate these mechanisms, we characterized transcriptomic changes in response to Al in roots of aspen (Populus tremula L.). Results: Aspen roots were treated with Al in solution culture for 6 h, 54 h, and 246 h. Transcriptomic changes were assessed by the Affymetrix GeneChip Poplar Genome Array. The analysis revealed 176 induced and 66 suppressed genes. The majority of these genes were regulated at 6 h, presumably reflecting root growth, which was strongly inhibited at 6 h and partially was recovered at 2 d and 10 d. Enrichment analysis identified sets of functionally related genes whose members were statistically over-represented compared to the genes on the microarray. These sets included genes related to cell wall modification, oxidative stress, cell death, and transport processes. Two of the genes involved in transport were related to the Arabidopsis Al tolerance genes AtALS3 (aluminum sensitive 3), possibly mediating redistribution of Al, and AtMATE (multi-drug and toxin extrusion), facilitating exudation of citrate. Expression patterns in response to Al in different plant tissues indicated that the two aspen genes are homologs of AtALS3 and AtMATE, suggesting that aspen and Arabidopsis share common mechanisms to cope with Al. Conclusion: This is the first survey of transcriptomic changes in response to Al in a forest tree. The results of our study provide a valuable set of data, which will help to further our understanding of the mechanisms and their regulation that enable aspen to grow in environments with toxic levels of Al. Aspen roots were treated with Al in solution culture for 6 h, 54 h, 246 h to cover a broad range of exposure times. Transcriptomic changes were assessed by the Affymetrix GeneChip Poplar Genome Array. For each time point, root tips of three independant plants were analyzed.

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	04A_2.csv	Csv
	04A_3.csv	Csv
	04B_1.csv	Csv
	04B_2.csv	Csv

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Populus metacaspases - The function of two type II metacaspases in woody tissues of Populus trees

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