Identifying sugarcane expressed sequences associated with nutrient transporters and peptide metal chelators

Abstract

Plant nutrient uptake is an active process, requiring energy to accumulate essential elements at higher levels in plant tissues than in the soil solution, while the presence of toxic metals or excess of nutrients requires mechanisms to modulate the accumulation of ions. Genes encoding ion transporters isolated from plants and yeast were used to identify sugarcane putative homologues in the sugarcane expressed sequence tag (SUCEST) database. Five cluster consensi with sequence homology to plant high-affinity phosphate transporter genes were identified. One cluster consensus allowed the prediction of a full-length protein containing 541 amino acids, with 81% amino acid identity to the Nicotiana tabacum NtPT1 gene, consisting of 12 membrane-spanning domains divided by a large hydrophilic charged region. Putative homologues to Arabidopsis thaliana micronutrient transporter genes were also detected in some of the SUCEST libraries. Iron uptake in grasses involves the release of the phytosiderophore mugeneic acid (MA) which chelate Fe 3+ which is then absorbed by a specific transporter. Sugarcane expressed sequence tag (EST) homologous to genes coding for three enzymes of the mugeneic acid biosynthetic pathway [nicotianamine synthase; nicotianamine transferase; and putative mugeneic acid synthetase (ids3)] and a putative Fe 3+ -phytosiderophore transporter were detected. Seven sugarcane sequence clusters were identified with strong homology to members of the ZIP gene family (ZIP1, ZIP3, ZIP4, IRT1 and ZNT1), while four clusters homologous to ZIP2 and three to ZAT were found. Homologues to members of another gene family, Nramp, which code for broad-specificity transition metal transporters were also detected with constitutive expression. Partial transcripts homologous to genes encoding γ-glutamylcysteine synthetase, glutathione synthetase, and phytochelatin synthase (responsible for biosynthesis of the metal chelator phytochelatin) and all four types of the major plant metal-chelator peptide metallothionein (MT) were identified: Type I MT being the most abundant (>1% of seed-library reads), followed by Type II which had a similar pattern of expression as that described for Arabidopsis MT. Identifying and understanding the expression of genes associated with nutrient uptake and metal tolerance could lead to the development of more nutrient-efficient sugarcane cultivars, or might allow the use of sugarcane as a hyper-accumulator plant for the restoration of contaminated areas in phytoremediation programs.

Sugarcane genes differentially expressed during water deficit

“…The metallothioneins are classified in four groups according to the distribution of the cysteine residues in their domains. All types of metallothioneins were identified in sugarcane, but the metallothioneins-type 1 was the most abundant and it showed a significant expression level in leaves (Figueira et al 2001). The identification of metallothioneins acting in the stress response in sugarcane is an indication that the control mechanisms of uptake and accumulation of essential and non-essential metals is important to plant stress tolerance.…”

Response of sugarcane to increasing concentrations of copper and cadmium and expression of metallothionein genes

“…Many plant MT genes were originally identified based on analyses of differential expression affected by various types of abiotic and biotic stresses (Snowden and Gardner, 1993;Choi et al, 1996;Fordham-Skelton et al, 1998;Ma et al, 2003) and/or developmental stages (Chatthai et al, 1997;Muñoz et al, 1998;Guo et al, 2003). Often, MT genes have been detected by large scale sequencing of expressed sequence tags (ESTs) (Figueira et al, 2001) or by serial analysis of gene expression (SAGE) (Matsumura et al, 1999;Gibbings et al, 2003), frequently as one of the most abundant transcripts (Cobbett and Goldsbrough, 2002). However, most of the predicted proteins have not been isolated, except for wheat (Lane et al, 1987) and Arabidopsis MTs (Murphy et al, 1997).…”

Análise de seqüências expressas em raízes de cana-de-açúcar colonizadas por Glomus clarum

“…Metalotioneínas tipo II são pouco abundantes em raízes de cana-de-açúcar, sendo encontradas em maior quantidade nas inflorescências (Figueira et al, 2001). Pouco se sabe sobre suas funções e sobre a regulação das diferentes isoformas.…”