Phytochrome Interaction with PP2A Phosphatases and its effects on Flower Initiation

All living things rely on energy to survive. These sources vary from species to species. For example, the main source of energy for humans and animals is food, and the main source of energy for plants is sunlight. Plants lack the ability to migrate to find energy sources, to escape from predators, or to avoid abiotic stress. Instead, they have a photoreceptor such as chlorophyll found in the chloroplasts of plants that absorb light and convert it into a cascade of electron transfer, which serves as a major energy source for plants.

Light is a signal that plants synchronize their internal clocks with the environment and are perceived by various photoreceptors. Red and blue light is absorbed by several plant pigments and cryptochrome. Phytochrome phyA is the main phytochrome of seedlings growing in the dark, but decomposes quickly under light to produce Cry1. Phytochrome B - E is more stable in phyB, the main phytochrome of seedlings grown under light. The cryptochrome (cry) gene is also a photosensitive component of the circadian clock, a photoreceptor, and is considered to be part of the clock's endogenous pacemaker mechanism. Cryptochromes 1-2 (included in blue-UVA) helps maintain the length of the clock cycle through lighting conditions

Protein phosphatase PP2A A1 requires dephosphorylation (and hence inactivation) of phot2 but apparently has no effect on phot1 dephosphorylation (Tseng and Briggs, 2010). 14-3-3 l Protein isoforms are necessary to achieve optimal pore opening mediated by phot 2, but do not affect pore opening mediated by phot 1. In addition, the mutation at the 14-3-31 locus had no effect on tropism via phot2, flattening of leaves or chloroplast movement (Tseng et al., 2012). Only phot1 mediates rapid inhibition of stem growth in yellowing seedlings (Folta and Spalding, 2001). Chloroplast evasion reaction and nuclear localization are regulated only by phot 2 (Demarsy and Fankhauser, 2009). Thus, many reactions can be activated by photofrin and have different sensitivities, but many other reactions depend only on one of the two photoreceptors. The phototin interaction protein necessary for the reaction is completely unnecessary for other reactions

Dephosphorylation of protein phosphatase reverses the effect of phosphorylation and assumes that the protein structure simply returns to its original conformation. Although phosphatases are far less than kinases, meaning they are less specific, it is known that some of them are regulated by phosphorylation or binding of effector molecules. Because phosphatases generally can recognize a number of phosphorylated protein substrates, we can target specific substrates by changing the mechanism of intracellular protein localization as necessary, as described elsewhere in this chapter I guess.