RESUMO
Feruloylation of arabinoxylan (AX) in grass cell walls is a key determinant of recalcitrance to enzyme attack, making it a target for improvement of grass crops, and of interest in grass evolution. Definitive evidence on the genes responsible is lacking so we studied a candidate gene that we identified within the BAHD acyl-CoA transferase family. We used RNA interference (RNAi) silencing of orthologs in the model grasses Setaria viridis (SvBAHD01) and Brachypodium distachyon (BdBAHD01) and determined effects on AX feruloylation. Silencing of SvBAHD01 in Setaria resulted in a c. 60% decrease in AX feruloylation in stems consistently across four generations. Silencing of BdBAHD01 in Brachypodium stems decreased feruloylation much less, possibly due to higher expression of functionally redundant genes. Setaria SvBAHD01 RNAi plants showed: no decrease in total lignin, approximately doubled arabinose acylated by p-coumarate, changes in two-dimensional NMR spectra of unfractionated cell walls consistent with biochemical estimates, no effect on total biomass production and an increase in biomass saccharification efficiency of 40-60%. We provide the first strong evidence for a key role of the BAHD01 gene in AX feruloylation and demonstrate that it is a promising target for improvement of grass crops for biofuel, biorefining and animal nutrition applications.
Assuntos
Biomassa , Parede Celular/metabolismo , Coenzima A-Transferases/genética , Ácidos Cumáricos/metabolismo , Genes de Plantas , Setaria (Planta)/enzimologia , Setaria (Planta)/genética , Supressão Genética , Ácidos/metabolismo , Brachypodium/genética , Metabolismo dos Carboidratos , Coenzima A-Transferases/metabolismo , Regulação da Expressão Gênica de Plantas , Inativação Gênica , Hidrólise , Lignina/metabolismo , Espectroscopia de Ressonância Magnética , Tamanho do Órgão , Filogenia , Caules de Planta/metabolismo , Plantas Geneticamente Modificadas , Sementes/anatomia & histologia , Sementes/crescimento & desenvolvimento , Transcriptoma/genética , Xilanos/metabolismoRESUMO
Acidic soils are distributed worldwide, predominantly in tropical and subtropical areas, reaching around 50% of the arable soil. This type of soil strongly reduces crop production, mainly because of the presence of aluminum, which has its solubility increased at low pH levels. A well-known physiological mechanism used by plants to cope with Al stress involves activation of membrane transporters responsible for organic acid anions secretion from the root apex to the rhizosphere, which chelate Al, preventing its absorption by roots. In sorghum, a membrane transporter gene belonging to multidrug and toxic compound extrusion (MATE) family was identified and characterized as an aluminum-activated citrate transporter gene responsible for Al tolerance in this crop. Setaria viridis is an emerging model for C4 species and it is an important model to validate some genes for further C4 crops transformation, such as sugarcane, maize, and wheat. In the present work, Setaria viridis was used as a model plant to overexpress a newly identified MATE gene from Brachypodium distachyon (BdMATE), closely related to SbMATE, for aluminum tolerance assays. Transgenic S. viridis plants overexpressing a BdMATE presented an improved Al tolerance phenotype, characterized by sustained root growth and exclusion of aluminum from the root apex in transgenic plants, as confirmed by hematoxylin assay. In addition, transgenic plants showed higher root citrate exudation into the rhizosphere, suggesting that Al tolerance improvement in these plants could be related to the chelation of the metal by the organic acid anion. These results suggest that BdMATE gene can be used to transform C4 crops of economic importance with improved aluminum tolerance.