A expressão de citocininas oxidases em raízes de arroz altera a morfologia radicular e aumenta a eficiência de aquisição de nutrientes

Abstract

The plant hormone cytokinin is known to be an important regulator of the plant root system. Research suggests that reduction in the amount of cytokinin in the root may lead to an increase in the size of the root system. Different strategies are used to reduce the amount of cytokinin in plant roots. In this work, the effect of over expression of genes encoding cytokinin oxidases (OsCKX) in root morphology and architecture of rice plants, as well as the efficiency of nutrient acquisition were studied. The OsCKX2 and OsCKX5 genes were fused to the promoter Rcc3 who runs a strong and specific expression in rice roots. Several strains of rice plants transformed with gene constructs were obtained PRcc3:OsCKX2:3xHA and PRcc3:OsCKX5:3xHA. Both constructions promoted desirable characteristics of root system morphology of the plants, such as: high volume, length, projection area and number of root tips. A greenhouse experiment was conducted with the plants PRcc3:OsCKX5:3xHA in a low fertility soil (Fragiudult) to evaluate the efficiency of nutrient acquisition and the root system morphological parameters. Expression of OsCKX5 gene under the control of the promoter Rcc3 resulted in an increase of more than 150 times in the expression of this gene in the roots of transformed plants compared to the untransformed plants; however, without affecting the levels of expression in the shoots. The specific expression in the root of OsCKX5 gene resulted in highest developed root system without compromising the growth of shoots. In general, the transformed plants (L #48 and L #49) showed biggest root mass, root depth and greater root/ shoot ratio. As a consequence, they showed to be most efficient in the absorption of macronutrients (N, P, K, Ca and Mg) and micronutrients (Fe and Zn), presenting highest levels and contents of these nutrients in the roots and leaves. The results indicate that the root-specific expression of the gene OsCKX5 results in increased root growth, and more efficient absorption of nutrients in low fertility soils.