Protein Phosphatase Activity and Acidic/Alkaline Balance as Factors Regulating the State of Phytochrome A and its Two Native Pools in the Plant Cell

Abstract

Phytochrome A (phyA), the most versatile plant phytochrome, exists in the two isoforms, phyA' and phyA'', differing by the character of its posttranslational modification, possibly, by phosphorylation at the N-terminal extension [Sineshchekov, V. (2010) J. Botany 2010, Article ID 358372]. This heterogeneity may explain the diverse modes of phyA action. We investigated possible roles of protein phosphatases activity and pH in regulation of the phyA pools' content in etiolated seedlings of maize and their extracts using fluorescence spectroscopy and photochemistry of the pigment. The phyA'/phyA'' ratio varied depending on the state of development of seedlings and the plant tissue/organ used. This ratio qualitatively correlated with the pH in maize root tips. In extracts, it reached a maximum at pH ≈ 7.5 characteristic for the cell cytoplasm. Inhibition of phosphatases of the PP1 and PP2A types with okadaic and cantharidic acids brought about phyA' decline and/or concomitant increase of phyA'' in coleoptiles and mesocotyls, but had no effect in roots, revealing a tissue/organ specificity. Thus, pH and phosphorylation status regulate the phyA'/phyA'' equilibrium and content in the etiolated (maize) cells and this regulation is connected with alteration of the processes of phyA' destruction and/or its transformation into the more stable phyA''.

The phosphatase/kinase balance affects phytochrome A and its native pools, phyA′ and phyA″, in etiolated maize roots: evidence from the induction of phyA′ destruction by a protein phosphatase inhibitor sodium fluoride

“…It was found that, in etiolated root tissues, NaF facilitated phyA′ destruction shifting the phyA′/phyA″ ratio towards phyA″ similarly to the effect of the specific inhibitors OA and CA in shoots, but with a lower extent, whereas in coleoptiles NaF was not active. This supports the notion [25] that the phosphorylation status of the cell regulates the phyA turnover in maize roots as well. However, the facts that NaF is active in roots, where the specific PP inhibitors, OA and CA, are inactive, whereas in stems the situation is reverse, suggest a different state of phyA and/or a different mechanism of action of the phyA destruction system in these organs.…”

“…Sodium fluoride (NaF) was used as a PP inhibitor with a wider range of the targets of its activity than the specific PP inhibitors (okadaic and cantharidic acids) previously employed in our experiments [25]. NaF is the source of the fluoride ions (F−) which irreversibly inhibit acidic serinethreonine phosphatases [28][29][30][31].…”

“…To verify this hypothesis and to try to find out if the phosphatase/kinase balance in the cell may affect the phyA′/phyA″ equilibrium, we have undertaken experiments with inhibitors of the Ser/Thr protein phosphatases (PP) of the PP1 and PP2A types active against phytochrome-okadaic and cantharidic acids (OA and CA). It was found that the phyA′/phyA″ proportion is indeed connected with the kinase/ phosphatase equilibrium in the tissues of etiolated maize seedlings [25]. The PP inhibition shifted the phyA′/phyA″ ratio towards the latter in etiolated maize stems at the expense of stimulated phyA′ destruction.…”

Tyrosine 263 in Cyanobacterial Phytochrome Cph1 Optimizes Photochemistry at the prelumi‐R→lumi‐R Step

“…Whereas in Pr the chromophore adopts a ZZZssa conformation, Pfr is ZZEssa due to photoisomerization at the C15 = C16 double bond, although recent structural studies have shown that the A and particularly the D rings are twisted relative to the B-C ring plain (5)(6)(7)(8)(9)(10). Interestingly, however, Pr in various phytochromes is heterogeneous, the different substates being associated with spectroscopic, photochemical and/or structural differences (10)(11)(12)(13)(14)(15)(16)(17)(18). No such heterogeneity has been reported for Pfr, however.…”

Histone Modification Is Involved in Okadaic Acid (OA) Induced DNA Damage Response and G2-M Transition Arrest in Maize

“…Okadaic acid (OA) is a powerful inhibitor of protein serine/threonine phosphatases-1 and -2A (PP1 and PP2A) [ 23 ]. It is widely adopted that treating plants such as maize to study the effect of PP1 and PP2A activities on signal transmitting and gene activation [ 24 , 25 ]. In addition, OA has also been widely used to alter the state of histone phosphorylation in cell cycle progression and is a very good agent for investigating the relationship between chromatin modification and cell cycle progression [ 26 , 27 ].…”