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

Abstract

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.

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

“…They are controlled primarily by phyA because light, which travels from stems to roots through the vascular tissue, is highly enriched with the farred component sensed exclusively by phyA. Our experiments with rice seedlings grown in darkness and under constant and pulsed far-red light (light conditions favorable for the HIR and VLFR response types, respectively) have shown that the downregulation of roots' growth is observed only under constant FR [12]. Taking in consideration that phyA″ and phyA′ mediate HIR and VLFR, respectively [9], we may conclude that this root growth rate reduction is controlled by phyA″, whereas phyA′ is inactive.…”

“…In the mutants, both constant FR and pulsed FR were active in rice roots' growth reduction, in contrast to the wild type where pulsed FR was inactive. This phyA activity in the mutants correlated with the higher phyA′ content and phyA′/ phyA″ proportion in them compared with the wild type [12]. This suggests that phyA′ is active in the mutants, but in the wild-type JA suppresses its activity.…”

“…Experiments with rice mutants deficient in the hormone jasmonic acid (JA) (hebiba and cpm2) have shown [12] that JA is intimately involved in the phyA activity in roots. In the mutants, both constant FR and pulsed FR were active in rice roots' growth reduction, in contrast to the wild type where pulsed FR was inactive.…”

“…On the contrary, rice phyA with the S/A substitution of 10 serines at the N-terminal extension (NTE) (expressed in transgenic Arabidopsis) is represented only by phyA″ [9], and the suppression of VLFR and promotion of HIR were observed in this transgenic plant by Kneissl et al [3]. Interestingly, the regulation of the phyA state and functions under R and FR light is accomplished in cooperation with the phytohormone jasmonic acid (JA) responsible for plant's reactions to wounding and infection [10][11][12].…”

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

“…In general, there is a very close connection between phyA functions and the hormonal status of the plant (see reviews [160][161][162][163][164][165][166]). We investigated the effects of the hormone jasmonic acid (JA) on the phyAs and their functions [167,168]. JA controls different aspects of plant growth and development, including inhibition of seed germination and root growth and stimulation of degradation of chloroplast proteins and leaf senescence (for review on JA see [160,[169][170][171]).…”