RuBisCO Depletion and Subcellular Fractionation for Enhanced Florigen Detection in Arabidopsis

In plants, complex signaling networks monitor and respond to environmental cues to determine the optimal time for the transition from the vegetative to reproductive phase. Understanding these networks requires robust tools to examine the levels and subcellular localization of key factors. The florigen FLOWERING LOCUS T (FT) is a crucial regulator of flowering time and occurs in soluble and membrane-bound forms. At low ambient temperatures, the ratio of these forms of FT undergoes a significant shift, which leads to a delay in the onset of flowering. To investigate these changes in FT localization, epitope-tagged FT protein can be isolated from plants by subcellular fractionation and its localization examined by immunoblot analysis of the resulting fractions. However, the highly abundant protein ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) can interfere with methods to detect and characterize low-abundance proteins such as FT. In this chapter, we present a method for analyzing the ratio of HA-tagged FT (HA:FT) in different subcellular fractions while mitigating the interference from RuBisCO by using protamine sulfate (PS) to deplete RuBisCO during protein purification, thereby enhancing HA:FT detection in fractionated samples.