Two Distinct Molecular Types of Phytochrome A in Plants: Evidence of Existence and Implications for Functioning

Phytochrome (phy) system in plants comprising a small number of phytochromes with phyA and phyB as major ones is responsible for acquiring light information in the red-far-red region of the solar spectrum. It provides optimal strategy for plant development under changing light conditions throughout all its life cycle beginning from seed germination and seedling establishment to fruiting and plant senescence. The phyA was shown to participate in the regulation of this cycle which is especially evident at its early stages. It mediates three modes of reactions-the very low and low fluence responses (VLFR and LFR) and the high irradiance responses (HIR). The phyA is the sole light receptor in the far-red spectral region responsible for plant's survival under a dense plant canopy where light is enriched with the far-red component. Its appearance is believed to be one of the main factors of plants successful evolution. So far, it is widely accepted that one molecular phyA species is responsible for its complex functional manifestations. In this review, the evidence of the existence of two distinct phyA types-major, light-labile and soluble phyAand minor, relatively light-stable and amphiphilic phyA-is presented as what may account for the diverse modes of phyA action.

Automated summary

The phytochrome (phy) system in plants, consisting of a small number of phytochromes with phyA and phyB as major ones, is responsible for detecting light in the red-far-red region of the solar spectrum. It plays a crucial role in plant development throughout all stages of its life cycle, from seed germination to senescence. PhyA is particularly involved in regulating this cycle, mediating three different types of reactions. It is the sole light receptor in the far-red spectral region, crucial for the survival of plants under a dense plant canopy. The existence of two distinct phyA types, major and light-labile, and minor and light-stable, may explain the diverse modes of phyA action.