The 2012 ASHS Annual Conference

Citrus trees were induced to flower by either exposure to low temperatures or water deficit. In the last decade, several genes considered to be involved in the regulation of flowering have been isolated and their expression characterized in response to low temperature in Citrus. However, reports on the effect of floral-inductive water deficit on the expression of flowering-related genes are lacking. In this work, the patterns of transcript accumulation of 4 flowering-related genes (CsFT, CsSL1, CsAP1, and CsLFY ) from Citrus sinensis were characterized during floral induction by water deficit. Exposure to water deficit increased the accumulation of CsFT in leaves whereas transcript levels of CsSL1, CsAP1, and CsLFY were slightly reduced for the duration of the treatment. However, when the water deficit was relieved, the accumulation of CsFT decreased sharply; and conversely, accumulation of CsSL1, CsAP1, and CsLFY transcripts increased. When floral-inductive water deficit and floral-inductive temperatures occurred at the same time, the increase in accumulation of CsFT, CsAP1, and CsLFY was larger than when water deficit occurred at non-floral inductive temperatures or at floral-inductive temperatures in well-watered trees. These results indicate that floral-inductive water deficit and low temperatures cause a similar response in the accumulation of transcripts of flowering-related genes suggesting that these genes could be ultimate targets of flowering signals initiated by both environmental stimuli that promote flowering in C. sinensis. Furthermore, in other species, these genes are key regulators of flowering in response to changes in photoperiod, vernalization and developmental age, suggesting that these genes could have evolved in plants to respond to a wide variety of flower-promoting signals from the environment. Responses of these genes in orange trees to gibberellins and day/night alternation will also be described.