Gene expression on Al3+ tolerance mechanisms comparing a Cerrado species (Qualea grandiflora) and lime (Citrus limonia cv. 'Cravo')

Abstract

The Brazilian savanna (Cerrado) presents edaphic peculiarities, such as soil acidity and high content of soluble aluminum (Al3+), so that species that are adapted to this type of environment exhibit effective strategies to deal with this stress. Aluminum is toxic to most plants, reducing root growth, causing disorder in the cytoskeleton and callose deposition, as well as reducing photosynthetic rates (caused by oxidation of thylakoid membranes). Several mechanisms of resistance or tolerance to high Al3+ concentrations in acidic soils have been reported; mainly those related to the exudation of organic acids that chelate Al3+, being such mechanisms absent (or poorly expressed) in sensitive species, such as the 'Rangpur' lime (Citrus limonia cv. 'Cravo'). Some Cerrado plants, such as Qualea grandiflora, exhibit tolerance to Al3+ by accumulating great amounts of Al3+ into leaf vacuoles, but keeping the proper root growth. This project aims to differentiate the metabolism of the 'Rangpur' lime (the most important rootstock for the Brazilian citrus industry) and of Q. grandiflora when cultivated under different concentrations of Al3+. For this, we will analyze the expression of genes related to the root Al3+ extrusion metabolism (synthesis of malate / citrate, channels ALMT / MATE), pectin methylation on the cell wall, Al3+ intracellular transport, and genes related to the biosynthesis of ethylene (Et) and auxin transport (IAA), also quantifying Et and IAA in root tips and, in addition, measuring the root growth. Thus, we will try to prove the Thesis that Al3+ benefits root development of Cerrado species, as opposed to agricultural species, whose root growth, which is mediated by IAA and Et, is limited by Al3+.