A half-type ABC transporter FeSTAR1 regulates Al resistance possibly via UDP-glucose-based hemicellulose metabolism and Al binding

Aims: Buckwheat (Fagopyrum esculentum) is highly tolerant to Al stress, but the molecular mechanisms remain largely unknown. This study aims to investigate a half-type ABC transporter gene (FeSTAR1) with respect to Al tolerance. Methods: The expression of FeSTAR1 was examined and complementation test in atstar1 mutant was conducted. Furthermore, Al distribution and cell wall polysaccharides content were analyzed. Results: FeSTAR1 is an ABC transporter protein with nucleotide binding domain, but lack of transmembrane domain. Consistently, FeSTAR1 is a soluble protein, localizing to both cytoplasm and nucleus. Al rapidly and specifically induced FeSTAR1 expression. Heterologous expression of FeSTAR1 in atstar1 rescued its Al tolerance, and exogenous applied UDP-glucose could alleviate Al sensitivity of atstar1 mutant, suggesting the connection between FeSTAR1 and UDP-glucose in terms of Al tolerance. Furthermore, FeSTAR1 complemented lines accumulated less Al in root cell wall than atstar1 mutant. Further cell wall fraction analysis showed that Al was largely confined to cell wall hemicellulose1, at which Al content was significantly lower in complemented lines. Consistent with Al distribution in different cell wall polysaccharides, complemented lines had lower hemicellulose1 content. Conclusion: Our results indicate that FeSTAR1 is involved in Al resistance via possibly cell wall matrix polysaccharides metabolism in buckwheat.