Genotypic differences in aluminium resistance in maize : inheritance, the role of cell-wall properties, and Al localization in the root apex

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Proteomic and phosphoproteomic analysis of polyethylene glycol-induced osmotic stress in root tips of common bean (Phaseolus vulgaris L.)

Previous studies have shown that polyethylene glycol (PEG)-induced osmotic stress (OS) reduces cell-wall (CW) porosity and limits aluminium (Al) uptake by root tips of common bean (Phaseolus vulgaris L.). A subsequent transcriptomic study suggested that genes related to CW processes are involved in adjustment to OS. In this study, a proteomic and phosphoproteomic approach was applied to identify OS-induced protein regulation to further improve our understanding of how OS affects Al accumulation. Analysis of total soluble proteins in root tips indicated that, in total, 22 proteins were differentially regulated by OS; these proteins were functionally categorized. Seventy-seven per- cent of the total expressed proteins were involved in metabolic pathways, particularly of carbohydrate and amino acid metabolism. An analysis of the apoplastic proteome revealed that OS reduced the level of five proteins and increased that of seven proteins. Investigation of the total soluble phosphoproteome suggested that dehydrin responded to OS with an enhanced phosphorylation state without a change in abundance. A cellular immunolocalization analysis indicated that dehydrin was localized mainly in the CW. This suggests that dehydrin may play a major protective role in the OS-induced physical breakdown of the CW structure and thus maintenance of the reversibility of CW extensibility during recovery from OS. The proteomic and phosphoproteomic analyses provided novel insights into the complex mechanisms of OS-induced reduction of Al accumulation in the root tips of common bean and highlight a key role for modification of CW structure.BMZ/GTZ/05.7860.9-001.00BMZ/GTZ/05.7860.9-001.0

Alteration of cell-wall porosity is involved in osmotic stress-induced enhancement of aluminium resistance in common bean (Phaseolus vulgaris L.)

Aluminium (Al) toxicity and drought are the two major abiotic stress factors limiting common bean production in the tropics. Using hydroponics, the short-term effects of combined Al toxicity and drought stress on root growth and Al uptake into the root apex were investigated. In the presence of Al stress, PEG 6000 (polyethylene glycol)-induced osmotic (drought) stress led to the amelioration of Al-induced inhibition of root elongation in the Al-sensitive genotype VAX 1. PEG 6000 (>> PEG 1000) treatment greatly decreased Al accumulation in the 1 cm root apices even when the roots were physically separated from the PEG solution using dialysis membrane tubes. Upon removal of PEG from the treatment solution, the root tips recovered from osmotic stress and the Al accumulation capacity was quickly restored. The PEG-induced reduction of Al accumulation was not due to a lower phytotoxic Al concentration in the treatment solution, reduced negativity of the root apoplast, or to enhanced citrate exudation. Also cell-wall (CW) material isolated from PEG-treated roots showed a low Al-binding capacity which, however, was restored after destroying the physical structure of the CW. The comparison of the Al3+, La3+, Sr2+, and Rb+ binding capacity of the intact root tips and the isolated CW revealed the specificity of the PEG 6000 effect for Al. This could be due to the higher hydrated ionic radius of Al3+ compared with other cations (Al3+ >> La3+ > Sr2+ > Rb+). In conclusion, the results provide circumstantial evidence that the osmotic stress-inhibited Al accumulation in root apices and thus reduced Al-induced inhibition of root elongation in the Al-sensitive genotype VAX 1 is related to the alteration of CW porosity resulting from PEG 6000-induced dehydration of the root apoplast

Physiological and molecular analysis of the interaction between aluminium toxicity and drought stress in common bean (Phaseolus vulgaris)

Aluminium (Al) toxicity and drought are two major factors limiting common bean (Phaseolus vulgaris) production in the tropics. Short-term effects of Al toxicity and drought stress on root growth in acid, Al-toxic soil were studied, with special emphasis on Al–drought interaction in the root apex. Root elongation was inhibited by both Al and drought. Combined stresses resulted in a more severe inhibition of root elongation than either stress alone. This result was different from the alleviation of Al toxicity by osmotic stress (–0.60 MPa polyethylene glycol) in hydroponics. However, drought reduced the impact of Al on the root tip, as indicated by the reduction of Al-induced callose formation and MATE expression. Combined Al and drought stress enhanced up-regulation of ACCO expression and synthesis of zeatin riboside, reduced drought-enhanced abscisic acid (ABA) concentration, and expression of NCED involved in ABA biosynthesis and the transcription factors bZIP and MYB, thus affecting the regulation of ABA-dependent genes (SUS, PvLEA18, KS-DHN, and LTP) in root tips. The results provide circumstantial evidence that in soil, drought alleviates Al injury, but Al renders the root apex more drought-sensitive, particularly by impacting the gene regulatory network involved in ABA signal transduction and cross-talk with other phytohormones necessary for maintaining root growth under drought

Transcriptomic analysis reveals differential gene expression in common bean (Phaseoulus vulgaris) for aluminum resistance

Common bean is the most important food legume in the world particularly for developing countries in the tropics, where it is produced on acid and Al-toxic soils. Al resistance in bean is known to be achieved through exudation of citrate from the root tip which chelates Al to a nontoxic form after a lag phase. Here we report on Al-induced transcriptional changes in the root tips of an Al-resistant bean cultivar using suppression subtractive hybridization. Four hours of Al treatment resulted in differential expression of a rage of genes. Genes involved in stress response, plant defense, signal transduction and translation were up-regulated while genes involved in metabolism were largely down-regulated. In addition, we also identified key genes involved in Al resistance. These include: voltage-dependent anion-selective channel, NADP-specific isocitrate dehydrogenase, Cytochrome P450 monooxygenase and F1-ATPase. The role of these genes in Al resistance is discussed

Aluminium-induced callose formation in root apices : inheritance and selection trait for adaptation of tropical maize to acid soils

International audienceAluminium (Al) toxicity limits maize production on acid soils of the tropics. However, wide genetic variation exists in maize for Al resistance. The objective of this study was to assess the Al resistance of open pollinated tropical maize cultivars, from widely differing origin, and their diallel crosses based on callose formation as a physiological marker, and study the inheritance and combining ability for Al resistance. Fifteen maize cultivars from 4 maize breeding programmes and their 105 crosses were grown under controlled environmental conditions in a growth chamber and treated without or with 25 μM Al at pH 4.3. After 12 h of A1 treatment, callose contents of 1 cm root apices were determined. There was a significant genotypic variation in callose formation under Al stress. Furthermore, diallel analysis indicated a significant general combining ability (GCA) but not specific combining ability (SCA), indicating that Al resistance is mainly controlled by additive genes. In general, Al-resistant cultivars showed favourable GCA effects while the sensitive cultivars had unfavourable GCA effects clearly indicating the dominant role of Al-resistant cultivars in the development or improvement of Al-resistant maize varieties. Moreover, a relatively high heritability (h[2] = 0.7) was obtained for Al resistance in nutrient solution. Aluminium resistance as revealed by callose content in Al-treated root apices was positively correlated to the relative grain yield of the same crosses evaluated across five tropical environments. In addition, strong genetic correlation was observed as GCA of callose formation in nutrient solution closely correlated with GCA of yield on acid soils. These findings suggest that Al-induced callose formation is a powerful tool to enhance the breeding of maize cultivars with superior adaptation to acid and Al-toxic soil

Transcriptomic analysis reveals differential gene expression in response to aluminium in common bean (Phaseolus vulgaris) genotypes

Background and Aims: Aluminium (Al) resistance in common bean is known to be due to exudation of citrate from the root after a lag phase, indicating the induction of gene transcription and protein synthesis. The aims of this study were to identify Al-induced differentially expressed genes and to analyse the expression of candidate genes conferring Al resistance in bean. Methods: The suppression subtractive hybridization (SSH) method was used to identify differentially expressed genes in an Al-resistant bean genotype ( Quimbaya ) during the induction period. Using quantitative real-time PCR the expression patterns of selected genes were compared between an Al-resistant and an Al-sensitive genotype ( VAX 1 ) treated with Al for up to 24 h. Key Results: Short-term Al treatment resulted in up-regulation of stress-induced genes and down-regulation of genes involved in metabolism. However, the expressions of genes encoding enzymes involved in citrate metabolism were not significantly affected by Al. Al treatment dramatically increased the expression of common bean expressed sequence tags belonging to the citrate transporter gene family MATE (multidrug and toxin extrusion family protein) in both the Al-resistant and -sensitive genotype in close agreement with Al-induced citrate exudation. Conclusions: The expression of a citrate transporter MATE gene is crucial for citrate exudation in common bean. However, although the expression of the citrate transporter is a prerequisite for citrate exudation, genotypic Al resistance in common bean particularly depends on the capacity to sustain the synthesis of citrate for maintaining the cytosolic citrate pool that enables exudation