Two modes of the light-induced phytochrome A decline--with and without changes in the proportion of its isoforms (phyA' and phyA''): evidence from fluorescence investigations of mutant phyA-3D pea

Applications of fluorescence spectroscopy in the investigation of plant phytochrome invivo

Fluorometry is an effective research tool in biology and medicine; it is widely used in the study of the photosynthetic pigment apparatus in vivo. This method can be applied to the key plant photoreceptor phytochrome (phy). The fluorescence of phytochrome in plants was recorded for the first time in the group of the author, and a spectrofluorometric technique for its in vivo study was developed. The photophysical and photochemical properties of the pigment were described, and the photoreceptor was shown to be present in plants as two phenomenological types-active (at cryogenic temperatures) and water-soluble (Pr') and inactive and amphiphilic (Pr″). The scheme of the photoreaction explaining their photochemical distinctions was proposed. Phytochrome A was shown to comprise both types (phyA' and phyA″), whereas phytochrome B was only the second type. For phyA', distinct conformers have been detected. phyA' and phyA″ differ by the N-terminus of the molecule, possibly by serine phosphorylation. They mediate, respectively, the very low fluence and high irradiance photoresponses. Light, internal factors (kinase/phosphatase balance, pH), and hormones (jasmonate) were shown to affect the content and functions of the two phyA pools. All this points to the effectiveness of the developed method for invivo investigations of the phytochrome system. The data obtained can be applied in practical terms in agrobiology and light culture, as well as in the use of phytochrome as a new nanotool and a fluorescent probe.

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 phyA' and minor, relatively light-stable and amphiphilic phyA″-is presented as what may account for the diverse modes of phyA action.

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 phyA′ and minor, relatively light-stable and amphiphilic phyA″—is presented as what may account for the diverse modes of phyA action.

Phytochrome A and its Functional Manifestations in Etiolated and Far‐red Light‐grown Seedlings of the Wild‐type Rice and its Hebiba and Cpm2 Mutants Deficient in the Defense‐related Phytohormone Jasmonic Acid

Interaction between phytochromes and hormones is becoming one of the major issues in plant photophysiology. In this work, effects of defense‐related jasmonic acid (JA) on phytochrome A (phyA) were investigated by fluorescence spectroscopy making use of two JA biosynthesis mutants of rice: cpm2 with the inactivated gene allene oxide cyclase and hebiba with additional genes deleted. Constant far‐red light (FRc) mediated by phyA reduced its content in the wild type (WT) and mutants, and brought about domination of its light‐stable pool (phyA″) in WT and light‐labile pool (phyA′) in the mutants. Pulsed FRp was much less effective. This FR effect classifies as primarily HIR with a low fluence threshold; it comprises inhibition of phyA biosynthesis, stimulation of phyA″→phyA′ transformation and phyA′ destruction. In the mutants, phyA suppresses [Pchlide] under FRp (VLFR) and stimulates it under FRc (HIR); these effects are lacking in WT. Similarly, phyA suppresses roots'growth under FRp in the mutants but not in WT. These JA mutant features suggest that JA reduces the phyA functional activity primarily in its phyA″ form mediating HIR. This modulating JA action on phyA functions under FR limiting their extreme manifestations may have contributed to the evolutionary advances of the land plants.

Phytochrome A and its Functional Manifestations in Etiolated and Far-red Light-grown Seedlings of the Wild-type Rice and its Hebiba and Cpm2 Mutants Deficient in the Defense-related Phytohormone Jasmonic Acid

Interaction between phytochromes and hormones is becoming one of the major issues in plant photophysiology. In this work, effects of defense-related jasmonic acid (JA) on phytochrome A (phyA) were investigated by fluorescence spectroscopy making use of two JA biosynthesis mutants of rice: cpm2 with the inactivated gene allene oxide cyclase and hebiba with additional genes deleted. Constant far-red light (FRc) mediated by phyA reduced its content in the wild type (WT) and mutants, and brought about domination of its light-stable pool (phyA″) in WT and light-labile pool (phyA') in the mutants. Pulsed FRp was much less effective. This FR effect classifies as primarily HIR with a low fluence threshold; it comprises inhibition of phyA biosynthesis, stimulation of phyA″→phyA' transformation and phyA' destruction. In the mutants, phyA suppresses [Pchlide] under FRp (VLFR) and stimulates it under FRc (HIR); these effects are lacking in WT. Similarly, phyA suppresses roots'growth under FRp in the mutants but not in WT. These JA mutant features suggest that JA reduces the phyA functional activity primarily in its phyA″ form mediating HIR. This modulating JA action on phyA functions under FR limiting their extreme manifestations may have contributed to the evolutionary advances of the land plants.

Two molecular species of phytochrome A with distinct modes of action

Adaptation of plants to environmental light conditions is achieved via operation of a highly complex photoreceptor apparatus. It includes the phytochrome system comprising phytochromes A and B (phyA and phyB) as the major components. phyA differs from phyB by several properties, including its ability to mediate all three photoresponse modes – the very low and low fluence responses (VLFR and LFR respectively) and the high irradiance responses (HIR), whereas phyB is responsible for LFR. This review discusses the uniqueness of phyA in terms of its structural and functional heterogeneity. The photoreceptor is presented in monocots and dicots by two native molecular species, phyAʹ and phyAʹʹ, differing by spectroscopic, photochemical and phenomenological properties. phyA differentiation into substates includes post-translational phosphorylation of a serine residue(s) at the N-terminal extension of the molecule with phyAʹ being the phosphorylated species and phyAʹʹ, dephosphorylated. They differ also by their mode of action, which depends on the cellular context. The current working hypothesis is that phyAʹ mediates VLFR and phyAʹʹ, HIR and LFR. The content and functional activity of the two pools are regulated by light and by phosphatase/kinase equilibrium and pH in darkness, what contributes to the fine-tuning of the phytochrome system. Detection of the native pools of the cryptogamic plant fern Adiantum capillus-veneris phy1 (phy1ʹ and phy1ʹʹ) similar to those of phyA suggests that the structural and functional heterogeneity of phyA is not a unique phenomenon and may have arisen earlier in the molecular evolution of the phytochrome system than the appearance of the angiosperm phytochromes.

Two molecular species of phytochrome A with distinct modes of action

Adaptation of plants to environmental light conditions is achieved via operation of a highly complex photoreceptor apparatus. It includes the phytochrome system comprising phytochromes A and B (phyA and phyB) as the major components. phyA differs from phyB by several properties, including its ability to mediate all three photoresponse modes - the very low and low fluence responses (VLFR and LFR respectively) and the high irradiance responses (HIR), whereas phyB is responsible for LFR. This review discusses the uniqueness of phyA in terms of its structural and functional heterogeneity. The photoreceptor is presented in monocots and dicots by two native molecular species, phyA' and phyA'', differing by spectroscopic, photochemical and phenomenological properties. phyA differentiation into substates includes post-translational phosphorylation of a serine residue(s) at the N-terminal extension of the molecule with phyA' being the phosphorylated species and phyA'', dephosphorylated. They differ also by their mode of action, which depends on the cellular context. The current working hypothesis is that phyA' mediates VLFR and phyA'', HIR and LFR. The content and functional activity of the two pools are regulated by light and by phosphatase/kinase equilibrium and pH in darkness, what contributes to the fine-tuning of the phytochrome system. Detection of the native pools of the cryptogamic plant fern Adiantum capillus-veneris phy1 (phy1' and phy1'') similar to those of phyA suggests that the structural and functional heterogeneity of phyA is not a unique phenomenon and may have arisen earlier in the molecular evolution of the phytochrome system than the appearance of the angiosperm phytochromes.

Two native types of phytochrome A, phyAʹ and phyAʺ, differ by the state of phosphorylation at the N-terminus as revealed by fluorescence investigations of the Ser/Ala mutant of rice phyA expressed in transgenic Arabidopsis

Phytochrome A (phyA) mediates different photoresponses what may be connected with the existence of its two types, phyAʹ and phyAʹʹ, differing by spectroscopic, photochemical and functional properties. We investigated a role of phyA phosphorylation in their formation turning to transgenic Arabidopsis thaliana (L. Heynh.) phyA or phyAphyB mutants overexpressing rice wild-type phyA (phyA WT) or mutant phyA (phyA SA) with the first 10 serines substituted by alanines. This prevents phyA phosphorylation at these sites and modifies photoresponses. Etiolated seedlings were employed and phyA parameters were evaluated with the use of low temperature fluorescence spectroscopy and photochemistry. Germination of seeds was induced by white light (WL) pre-treatment for 15 min or 3 h. Emission spectra of rice phyA WT and phyA SA were similar and their total content was comparable. However, the phyAʹ/phyAʹʹ proportion in phyA WT was high and varied with the duration of the WL pre-treatment, whereas in phyA SA it was substantially shifted towards phyAʹʹ and did not depend on the pre-illumination. This suggests that phyA SA comprises primarily or exclusively the phyAʹʹ pool and supports the notion that the two phyA types differ by the state of serine phosphorylation. phyAʹʹ was also found to be much more effective in the germination induction than phyAʹ.

Two native types of phytochrome A, phyA' and phyA", differ by the state of phosphorylation at the N-terminus as revealed by fluorescence investigations of the Ser/Ala mutant of rice phyA expressed in transgenic Arabidopsis

Phytochrome A (phyA) mediates different photoresponses what may be connected with the existence of its two types, phyA' and phyA'', differing by spectroscopic, photochemical and functional properties. We investigated a role of phyA phosphorylation in their formation turning to transgenic Arabidopsis thaliana (L. Heynh.) phyA or phyAphyB mutants overexpressing rice wild-type phyA (phyA WT) or mutant phyA (phyA SA) with the first 10 serines substituted by alanines. This prevents phyA phosphorylation at these sites and modifies photoresponses. Etiolated seedlings were employed and phyA parameters were evaluated with the use of low temperature fluorescence spectroscopy and photochemistry. Germination of seeds was induced by white light (WL) pre-treatment for 15min or 3h. Emission spectra of rice phyA WT and phyA SA were similar and their total content was comparable. However, the phyA'/phyA'' proportion in phyA WT was high and varied with the duration of the WL pre-treatment, whereas in phyA SA it was substantially shifted towards phyA'' and did not depend on the pre-illumination. This suggests that phyA SA comprises primarily or exclusively the phyA'' pool and supports the notion that the two phyA types differ by the state of serine phosphorylation. phyA'' was also found to be much more effective in the germination induction than phyA'.

Fluorescence and Photochemical Investigations of Phytochrome in Higher Plants

In higher plants, photoreceptor phytochrome (phy)—photoisomerizing biliprotein working as a light-driven molecular switch—is represented by a small family of phytochrome gene products with phyA and phyB as major species. phyA is unique among other phytochromes mediating photoresponse modes specific only for this pigment (far-red light induced) and also photoresponses characteristic of phyB and other minor phys (red light induced). In our group,in vivofluorescence investigations of phytochrome were initiated and two native phyA pools—posttranslationally modifiedPHYAgene products designated phyA′and phyA″—were detected in dicots and monocots. They differ by spectroscopic and photochemical parameters, by abundance and distribution in etiolated plant tissues, by light stability, and other phenomenological characteristics, and, most importantly, by their functional properties. This may explain, at least partially, the nature of the uniqueness of the phyA action. In this paper, the data on the phyA polymorphism are summarized with attention to the applied experimental approach.

Two Native Pools of Phytochrome A in Monocots: Evidence from Fluorescence Investigations of Phytochrome Mutants of Rice

Fluorescence investigations of phytochrome (phy) in rice (Oryza sativa L. cv. Nipponbare) mutants deficient in phyA, phyB and phyA plus phyB were performed. Total content of the pigment (Ptot) and its spectroscopic and photochemical characteristics were determined in different parts of the dark‐grown and far‐red light (FR)‐grown coleoptiles. Spectroscopically, phyA in the phyB mutant was identical to phyA in the wild‐type (WT) and the extent of the conversion from Pr to lumi‐R at 85 K was the same for phyA in both lines and varied similarly, depending on the part of the coleoptile used. The latter finding proved that phyA in rice is heterogeneous and comprises two phyA populations, phyA′ and phyA″. Functional properties of phyA were also determined. In the dark the phyB mutant had a higher content of phyA, inactive protochlorophyllide (Pchlide633) and active protochlorophyllide (Pchlide655) than WT and its coleoptile was longer, indicating that phyB may affect the development of WT seedlings in the dark. Constant FR drastically reduced the content of phyA, Pchlide633 and Pchlide655 and brought about coleoptile shortening and appearance of the first leaf, whereas pulsed FR of equal fluence was less effective. This suggested that the reactions were primarily of the high irradiance responses type, which are likely to be mediated by phyA′. The effects on protochlorophyllide biosynthesis and growth responses type were more pronounced in the phyB mutant than in the WT seedlings, which can be connected with the higher phyA′ content in the phyB mutant and/or phyB interference with its action in WT seedlings. In the phyA mutant induction of Pchlide633 and Pchlide655 biosynthesis was observed under constant FR, indicating that phyC may be responsible for this effect.

Two Native Pools of Phytochrome A in Monocots: Evidence from Fluorescence Investigations of Phytochrome Mutants of Rice

Fluorescence investigations of phytochrome (phy) in rice (Oryza sativa L. cv. Nipponbare) mutants deficient in phyA, phyB and phyA plus phyB were performed. Total content of the pigment (P(tot)) and its spectroscopic and photochemical characteristics were determined in different parts of the dark-grown and far-red light (FR)-grown coleoptiles. Spectroscopically, phyA in the phyB mutant was identical to phyA in the wild-type (WT) and the extent of the conversion from Pr to lumi-R at 85 K was the same for phyA in both lines and varied similarly, depending on the part of the coleoptile used. The latter finding proved that phyA in rice is heterogeneous and comprises two phyA populations, phyA' and phyA". Functional properties of phyA were also determined. In the dark the phyB mutant had a higher content of phyA, inactive protochlorophyllide (Pchlide633) and active protochlorophyllide (Pchlide655) than WT and its coleoptile was longer, indicating that phyB may affect the development of WT seedlings in the dark. Constant FR drastically reduced the content of phyA, Pchlide633 and Pchlide655 and brought about coleoptile shortening and appearance of the first leaf, whereas pulsed FR of equal fluence was less effective. This suggested that the reactions were primarily of the high irradiance responses type, which are likely to be mediated by phyA'. The effects on protochlorophyllide biosynthesis and growth responses type were more pronounced in the phyB mutant than in the WT seedlings, which can be connected with the higher phyA' content in the phyB mutant and/or phyB interference with its action in WT seedlings. In the phyA mutant induction of Pchlide633 and Pchlide655 biosynthesis was observed under constant FR, indicating that phyC may be responsible for this effect.

The jasmonate-free rice mutant hebiba is affected in the response of phyA′/phyA″ pools and protochlorophyllide biosynthesis to far-red light

Phytochrome (phy) A in its two native isoforms (phyA' and phyA") and the active (Pchlide(655)) and inactive (Pchlide(633)) protochlorophyllides were investigated by low-temperature fluorescence spectroscopy in the tips of rice (Oryza sativa L. Japonica cv Nihonmasari) coleoptiles from wild type (WT) and the jasmonate-deficient mutant hebiba. The seedlings were either grown in the dark or under pulsed (FRp) or continuous (FRc) far-red light (lambda(a) >/= 720 nm) of equal fluences. In the dark, the mutant had a long mesocotyl and a short coleoptile, whereas the situation was reversed under FR: short mesocotyl and long coleoptile, suggesting that the effect is mediated by phyA. Under these conditions the WT displayed a short coleoptile and emergence of the first leaf. In the dark, the spectroscopic and photochemical properties of phyA, its content and the proportion of its two pools, phyA' and phyA", were virtually identical between WT and hebiba. However, the total content of protochlorophyllides was higher in the mutant. Upon illumination with FRc, [phyA] declined in the WT and the ratio between phyA' and phyA" shifted towards phyA". In hebiba, the light-induced decline of [phyA] was less pronounced and the ratio between phyA' and phyA" did not shift. Moreover, in the WT, FRp stimulated the biosynthesis of Pchlide(655), whereas FRc was inhibiting. In contrast, in the mutant, both FRp and FRc stimulated the synthesis of Pchlide(655). This means that FRc caused the opposite effect in hebiba. This difference correlates with a slower photodestruction of primarily the light-labile phyA' pool in hebiba.