18/12/18 |   Plant production  Coping with Droughts

Researchers identify sorghum genes that potencialize tolerance to aluminum

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Photo: Eugênia Ribeiro

Eugênia Ribeiro -

Research by Embrapa in partnership with the Federal University of Viçosa (UFV) identified two new genes that potencialize the plant's tolerance to aluminum in sorghum crops. The Brazilian discovery was reported in the paper published in the paper published cado in the journal Proceedings of the National Academy of Sciences of the USA (PNAS), entitled “Repeat variants for the SbMATE transporter protect sorghum roots from aluminum toxicity by transcriptional interplay in cis and trans”. The two genes that were identified potencialize the effect of a third one called SbMATE, which makes plants tolerate toxic aluminum in acid soils.

These two isolated genes, which are called transcription factors, work as a sensor: in the presence of aluminum, the expression of both increases, precisely when tolerance to the element is needed. In the absence of the chemical element, their expression is reduced, and so is the expression of the SbMATE gene.

“We believe that this is the result of an evolutionary mechanism to prevent the loss of energy in the form of organic carbon when there is no aluminum stress”, clarifies the Embrapa Maize and Sorghum researcher Jurandir Vieira de Magalhães, who led the research in partnership with professor Elizabeth Fontes, from the Federal University of Viçosa (UFV).

This result is especially important because the soils in the Brazilian Cerrado regions are acid, with the presence of aluminum, which damages the plants' root system and reduces crop productivity. Besides Brazil, this problem is also very common in tropical regions, like large portions of Africa and Asia.

More tolerance to droughts

Crop tolerance to aluminum has a close relationship with the plant's capacity to also tolerate drought, as, when the roots are damaged by aluminum, they are do not grow deep into the soil. A damaged root system reduces the plant's water and nutrient absorption capacity, which causes loss of productivity in the farms. This problem is particularly common in dry spells, which frequently occur in the Brazilian Cerrado region.

“In fact, at Embrapa, during the work of identifying cultivars that would be more tolerant to droughts, over 20 years ago the first aluminum-tolerant materials were identified by the researchers Robert Schaffert, in sorghum breeding, and Elton Gama and Ricardo Magnavacca, in maize breeding.”, Magalhães recalls.

Advance in the breeding process

The research also aimed to generate a technology that would allow the molecular diagnosis of aluminum tolerance even in a gene bank, with hundreds or even thousand of accessions, facilitating the work of the breeders in the identification of sources of tolerance.

This result can be used to direct crossings in breeding and genetic improvement programs, in order to facilitate the production of aluminum-tolerant cultivars. “In the end, the study has composed a genetic information system. Now, with the knowledge about such genes, making new molecular essays, we can recommend the crossings that should be made for the development of aluminum-tolerant sorghum cultivars for cultivation in acid soils to breeders with more precision.”

Magalhães underscores two impacts of the work. “Now, considering the new genes, we are more able to predict whether a genotype is going to be tolerant or sensitive to aluminum, and can also maximize the SbMATE gene's efficiency in increasing the productivity of sorghum cultivated in acid soils”, the scientist celebrates.

The discovery of the fundamental gene for the crops

According to Magalhães, the research on plant tolerance to aluminum toxicity at Embrapa has already been going on for decades and, since 2002, scientists have invested in cloning the genes related to this trait.

“A cloning study concluded in 2007 resulted in the identification of SbMATE, the first gene for aluminum tolerance to be isolated in sorghum and the second one identified in plants. The work was carried out by Embrapa Maize and Sorghum in partnership with the University of Cornell, the United States Department of Agriculture (USDA) and the University of Texas A&M”, reports the Embrapa scientist, recalling that the result was published in the journal Nature Genetics.

Based on such knowledge, Embrapa Maize and Sorghum investigated the effect of this gene in grain yield in acid soils. “Despite having previously isolated the SbMATE gene, we had not quantified its effect on sorghum production in soils with aluminum toxicity in detail. We then published another paper in 2016, showing that the gene causes a productivity increase of a ton per hectare in sorghum under aluminum toxicity in the soil. We have concluded that, to cultivate sorghum in Cerrado soil conditions, it is fundamental to have this gene in the crop”, he declares.

However, the scientists later found materials that should be tolerant to aluminum, because of the SbMATE gene action, but presented less tolerance than expected or were even sensitive to the element. “There was a certain amount of frustration, as the technique worked, but not as perfectly as we hoped. Then we raised the hypothesis that the SbMATE gene probably did not work alone. Perhaps it needed other genes to control its expression, potencializing its effect on aluminum tolerance”, Magalhães recalls.

That was precisely the content of the discovery now published at the PNAS journal. The research identified two other genes that interact with the gene cloned in 2007 and potencialize its action in aluminum tolerance. “The identification of these two new genes was a fundamental point in the study. In very simple terms, the genes have a DNA sequence that precedes the gene itself called promoter region, which controls gene expression. The expectation is that the higher the expression of a gene, the greater the amount of the protein codified by such gene, which will influence the different traits controlled by the genes, such as, for instance, the aluminum tolerance controlled by the SbMATE gene.”

In other words, the genes can be more or less expressed, depending on the variables present in the promoter regions. For example, human cells contain the complete set of human body genes. However, some of them can be linked to certain cells and others be turned off, or there can be variations in the gene expression, in given kinds of tissue and certain conditions. This contributes to organ differentiation, among other things.

The Embrapa researcher explains that the same comparison can be made with the genes for aluminum tolerance. The SbMATE gene is much more often expressed at the root tip than in other regions of the roots, and it is precisely the root apex that has to be protected from aluminum so that the root system grows well even in the presence of the metal. (see the difference in the picture above).

Translation: Mariana Medeiros

Sandra Brito (MTb 06230/MG)
Embrapa Maize and Sorghum

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