学位報告

学位報告４
報告番号

※甲第号

主論

文の要旨

論文題目

The family of Pseudo Response Regulator genes (PRR)
in the moss Physcomitrella patens.（蘚類ヒメツリガネ
ゴケにおける Pseudo Response Regulator 遺伝子族）

氏

Santosh Balasaheb Satbhai

名論 文 内 容 の 要 旨
The PRR genes play a central role in the flowering plant A. thaliana circadian clock.
To address the question of the origin of PRRs, this gene family was analyzed in the moss P.
patens, a phylogenetically distant organism.
In A. thaliana, O. sativa (rice), and all other higher plants five PRR homologs exist(TOC1/PRR1, PRR3, PRR5, PRR7, and PRR9). Four PRR homologs were found in P.
patens, suggesting that this gene family has ancient origins in the plant kingdom. However,most striking difference observed in the case of P. patens, P. patens is the first land plants
so far studied in that TOC1 ortholog is absent. Further analysis demonstrated that, all
PpPRRs forms separate cluster in phlogenteic tree and they showed close relationship withhigher plant PRR7/3 group. Another striking difference found in PpPRRs that, they all
retained potential phosphoaccpetor residue similarly as RRs, consistent with this PpPRR2
protein underwent phosphotransfer in an in-vitro phosphorlyation assay. An essential featureof PRRs function in A. thalaina is a circadian controlled rhythm of transcript abundance andthey are core clock components in A. thaliana circadian clock. The related PpPRRs are also
found to be under the control of circadian clock, they all showed robust diurnal rhythms inLD (12L: 12D) and endogenous circadian rhythms in DD (continuous dark) conditions.
Interestingly, the expression of each PpPRR gene only showed significant rhythmicity inconstant darkness, not in constant light. This is in contrast with their respective A. thaliana
homologs, the transcript levels of which showed robust circadian rhythms in continuouslight. Moreover, all PpPRRs showed acute light responses to all light types, suggesting theirrole in light signaling.
In PpCCA1a/1b double disruptant all PpPRRs showed higher expression in light
condition, suggesting their expression was suppressed by PpCCA1a/1b in presence of light.
Similar negative regulation of PpPRRs by PpCCA1a/1b was already found in their A.
thaliana counterparts, suggesting the conservation of clock systems in two distantly relatedspecies.
The functional similarities of PpPRRs and AtPRRs were assessed by misexpressing

学位関係

PpPRR2 gene in A. thaliana. PpPRR2 misexpressiong A. thaliana plants exhibited thephenotypes of short period rhythm in continuous dark, early flowering in short day, short
hypocotyls in short day and hypersensitivity to red light during early photomorphogenesis,
compared with the wild type plants. Similar events were previously demonstrated when theA. thaliana clock-associated PRR were misexpressed. These similarities provide conclusive
evidence that these genes have similar functions as clock components. Therefore, thegenetic structures of the circadian oscillators are likely conserved between early land plantand flowering plants; in short the core clock components of circadian systems are likely
conserved among land plants.
The results of this study clearly supported the view that plant PRRs are indeed theevolutionarily conserved crucial clock components. To further confirm this idea; more direct
experiments are requirement, including characterization of multiple loss-of-function mutantsof PpPRRs in the moss. In a future study, in parallel with gene knock out experiments, it
should also be addressed whether PpPRRs are involved in phosphotransfer functions inplanta. Moreover, a HK(s) and a HPt(s) that are partners to (at least some of) PpPRR
proteins should be characterized. It might not be easy to identify a partner HK(s) because
the P. patens genome contains as many as ~31 HK sequences (Ishida et al., 2010), unlike A.
thaliana, which contains only 8 HK genes (Hwang et al., 2002). However, the availabilityof the entire genome sequence, many full-length cDNA clones and the feasibility of genefunctional analysis based on gene targeting techniques will support the identification of such
HK and HPt genes in P. patens, possibly as novel clock genes.

38 字×23 行