Perspectivas sobre o florescimento da cana-de-açúcar: integrando fotoperíodo e metabolismo energético

Abstract

Flowering is a limiting factor to sugarcane production because it impairs the storage of sucrose and, consequently, the crop yield.The photoperiod is the main environmental factor responsible for the floral induction in sugarcane. The transition to the reproductive stage is controlled by endogenous and environmental signals that induce the expression of flowering integrating genes. Among these genes, FLOWERING LOCUS T (FT) stands out: its transcription occurs as a function of day length alterations. In both monocotyledons and dicotyledons genes homologous to FT act in floral induction and their expression is considered limiting in flowering promotion. The photoperiod, together with the circadian clock promotes changes at molecular levels, leading to the expression of genes involved in floral induction, and at physiological and biochemical levels. Among the provoked alterations is the carbohydrate metabolism, which initially can act in the flowering induction and later, in sugarcane, causes a loss of productivity. Sucrose and other intermediates of carbohydrate metabolism, such as trehalose and enzymes involved in its synthesis, may act to induce flowering. Homologous genes to TPS (STPSI and STPSII) and to FT have already been identified in sugarcane, and possibly, some of these FT homologues play a key role in the floral induction of this plant through photoperiod and may or may not act together as genes homologous to TPS. In this sense, the purpose of this work was to understand the process of floral induction through photoperiod and its relations with carbohydrate metabolism.We have done in silico analysis of possible orthologues of FT in sugarcane, characterization of qualitative expression in different plant tissues and characterization of quantitative expression of the putative flowering promoter ScFT6 both throughout the day and in sugarcane cultivars contrasting in relation to flowering. Besides that, sugarcane plants were submitted to two photoperiod conditions (shortening day and elongating day). During these treatments, gas exchanges were analyzed throughout the conduction period of the assay, as well as real-time expression of ScFT6, SPSI and SPSII genes and determination of the contents of reducing sugars (starch and sucrose). Among the possible FT homologues identified in sugarcane, stands out the ScFT6 gene, which has a conserved domain sequence and amino acids at characteristic positions of blossoming inducing PEBP family genes. The expression of the ScFT6 gene, like other flowering inducersFTs found in other species, occurs in mature leaves and shoot apexbeen controlled by the circadian rhythm. Varieties with distinct behavior for flowering have variable expression of the ScFT6 gene. Reduction in day length, responsible for flowering induction in sugarcane through photoperiod, increases expression of the putative flowering promoter ScFT6, besides promoting the increase in expression of STPSII, sign of carbon status of the plant. The expression of ScFT6 gene was not correlated to carbohydrate levels in sugarcane plants. Possibly it acts in the flowering induction exclusively by the luminous signal transmission.