Enhanced aluminum tolerance in sugarcane: evaluation of SbMATE overexpression and genome-wide identification of ALMTs in Saccharum spp

Abstract

Background: A major limiting factor for plant growth is the aluminum (Al) toxicity in acidic soils, especially in tropical regions. The exclusion of Al from the root apex through root exudation of organic acids such as malate and citrate is one of the most ubiquitous tolerance mechanisms in the plant kingdom. Two families of anion channels that confer Al tolerance are well described in the literature, ALMT and MATE family.

Results: In this study, sugarcane plants constitutively overexpressing the Sorghum bicolor MATE gene (SbMATE) showed improved tolerance to Al when compared to non-transgenic (NT) plants, characterized by sustained root growth and exclusion of aluminum from the root apex based on the result obtained with hematoxylin staining. In addition, genome-wide analysis of the recently released sugarcane genome identified 11 ALMT genes and molecular studies showed potential new targets for aluminum tolerance.

Conclusions: Our results indicate that the transgenic plants overexpressing the Sorghum bicolor MATE has an improved tolerance to Al. The expression profile of ALMT genes revels potential candidate genes to be used has an alternative for agricultural expansion in Brazil and other areas with aluminum toxicity in poor and acid soils.

Keywords: ALMT; Abiotic stress; Aluminum; Hydroponic system; MATE; Sugarcane.

Fig. 1

Maximum likelihood phylogeny of ALMTs in sugarcane and of plants. The bootstap values are represent in color branch scale and values > 70 are highlighted in the figure

Fig. 2

Intron/exon pattern of SoALMT gene. Exons and introns are shown as yellow boxes and thin lines, respectively

Fig. 3

Sugarcane transgenic events overexpressing SbMATE and NT plants in the absence (−Al; left panel) and after 2 weeks and six weeks of exposure to {505.9} μM Al³⁺ (+Al; right panel)

Fig. 4

Relative Root Net Growth of sugarcane transgenic events SbMATE and NT plants grown under the absence (−Al) or presence (+Al) of {505.9} μM Al³⁺ over six weeks. The length of the roots was measured before and after each week of growth in the Hoagland’s half concentration solution with (+Al) and without (−Al) aluminum (n = 6 plantlets). *Significantly different at p < 0.05 between NT and transgenic plants

Fig. 5

(a) Hematoxylin staining after 24 h exposure to {505.9} μM Al³⁺ in root tips of sugarcane transgenic events overexpressing SbMATE and NT plant. (b) Citrate and malate abundance on root exudates in the absence and after 12 days of exposure to {505.9} μM Al³⁺. The organic acids were determined by gas chromatography/mass spectrometry (GC/MS). The data are represented by fold-change of the organic acids in transgenic events compared to control plants. *Significantly different at p < 0.001 between NT and transgenic plants

Fig. 6

Relative gene expression of the SoALMTs in the NT and transgenic events submitted to {0} and {505.9} μM Al³⁺ after six weeks. *Significantly different at p < 0.05 between ­Al and + Al treatments in transgenic plants. Vertical bars show ± S.E. for n = 3

Fig. 7

Relative gene expression levels of the SoCSY (CSY), SoMDH (MDH), SoFUM (FUM), SoSTOP1, SoSTAR1 and SoNRAT1 in the sugarcane transgenic events and NT plants submitted to {0} and {505.9} μM Al³⁺ after seven weeks. *Significantly different at p < 0.05 between ­Al and + Al treatments of the NT and transgenic plants. Vertical bars show ± S.E. for n = 3