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

Photochem & Photobiology

Koppel

Riemann

et al. 2020

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.

Section: Discussionmentioning

confidence: 66%

Section: Discussionmentioning

confidence: 99%

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

Photochem & Photobiology

Koppel

Riemann

et al. 2020

“…Because the FRc illumination is a key feature of the HIR (1), we may attribute this negative autoregulation of phyA to this photoresponse type. Earlier, it was found that the effect of FRc on the phyA concentration in wheat (20) and the pea (25) is mediated by phyA′ and we may hypothesize that this phyA species plays the same role in rice.…”

Section: Discussionmentioning

confidence: 82%

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

Photochem & Photobiology

Loskovich

Inagaki

et al. 2006

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.

“…Note also a much lower effect of Rc and a much higher effect of FRc on the total phytochrome content in the case of the pea mutant suggesting that this mutation makes the photoreceptor less lightlabile and more physiologically active. (From [87,88]). supported by the same mode of phyA decline (without the phyA /phyA ratio violation) observed even without FRc illumination in the epicotyls of the "de-etiolated" lip mutant of pea ( Figure 17) [89].…”

Section: Functional Distinctions Betweenmentioning

confidence: 99%

“…In the context of the contrasting phyA and phyA functional properties of particular interest is the fact that their content in the plant is differentially regulated by red and far-red light. Constant illumination by R (Rc) of dark-grown seedlings (of pea) caused a gross decline in the total phyA content and a shift in the equilibrium towards the more light-stable phyA due to a destruction primarily of the light-labile phyA [39] whereas in the case of the constant far-red illumination of growing seedlings there was a considerable total phyA decline which was not followed by a violation in the equilibrium of its pools [87] ( Figure 16). The nature of the effects of Rc and FRc on phyA and its pools was investigated using the point-mutated phyA-3D pea with the substitution A194V [87,88].…”

Section: Functional Distinctions Betweenmentioning

confidence: 99%

Fluorescence and Photochemical Investigations of Phytochrome in Higher Plants

2010

Journal of Botany

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 vivo fluorescence investigations of phytochrome were initiated and two native phyA pools—posttranslationally modified PHYA gene 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.