PIF1 Regulates Plastid Development by Repressing Photosynthetic Genes in the Endodermis

Mutations in Phytochrome Interacting Factors （PIFs） induce a conversion of the endodermal amyloplasts necessary for gravity sensing to plastids with developed thylakoids accompanied by abnormal activation of photosynthetic genes in the dark. In this study, we investigated how PIFs regulate endodermal plastid development by performing comparative transcriptome analysis. We show that both endodermal expression of PIF1 and global expression of the PIF quartet induce transcriptional changes in genes enriched for nuclear-encoded photosynthetic genes such as LHCA and LHCB. Among the 94 shared differentially expressed genes identified from the comparative transcriptome analysis, only 14 genes are demonstrated to be direct targets of PIF1, and most photosynthetic genes are not. Using a co-expression analysis, we identified a direct target of PIF, whose expression pattern shows a strong negative correlation with many photo- synthetic genes. We have named this gene REPRESSOR OF PHOTOSYNTHETIC GENES1 （RPGE1）. Endodermal expression of RPGE1 rescued the elevated expression of photosynthetic genes found in the pff quadruple （pifQ） mutant and partly restored amyloplast development and hypocotyl negative gravitropism. Taken together, our results indicate that RPGE1 acts downstream of PIF1 in the endodermis to repress photosynthetic genes and regulate plastid development.

Characterization of ribulose-1,5-bisphosphate carboxylase/oxygenase and transcriptional analysis of its related genes in Saccharina japonica(Laminariales,Phaeophyta)

Saccharina japonica is a common macroalga in sublittoral communities of cold seawater environments, and consequently may have highly efficient ribulose-1, 5-bisphosphate carboxylase/ oxygenase （Rubisco） activity for carbon assimilation. In our study, we cloned the full-length Rubisco gene from S.japonica （SJ-rbc）. It contained an open reading frame for a large subunit gene （SJ-rbcL） of 1 467 bp, a small subunit gene （SJ-rbcS） of 420 bp, and a SJ-rbcL/S intergenie spacer of 269 bp. The deduced peptides of SJ-rbcL and SJ-rbcS were 488 and 139 amino acids with theoretical molecular weights and isoelectric points of 53.97 kDa, 5.81 and 15,84 kDa, 4.71, respectively. After induction with 1 mmol/L isopropyl-β-D- thiogalactopyranoside for 5 h and purification by Ni2＋ affinity chromatography, electrophoresis and western blot detection demonstrated successful expression of the 55 kDa SJ-rbcL protein. Real-time quantitative PCR showed that the mRNA levels of SJ-rbcL in gametophytes increased when transferred into normal growth conditions and exhibited diurnal variations： increased expression during the day but suppressed expression at night. This observation implied that Rubisco played a role in normal gametophytic growth and development. In juvenile sporophytes, mRNA levels of SJ-rbcL, carbonic anhydrase, Calvin-Benson- Bassham cycle-related enzyme, and chloroplast light-harvesting protein were remarkably increased under continuous light irradiance. Similarly, expression of these genes was up-regulated under blue light irradiance at 350 umol/（m2.s）. Our results indicate that long-term white light and short-term blue light irradiance enhances juvenile sporophytic growth by synergistic effects of various photosynthetic elements.

The Dof transcription factor COG1 acts as a key regulator of plant biomass by promoting photosynthesis and starch accumulation

Photosynthetic efficiency is the primary determinant of crop yield,including vegetative biomass and grain yield.Manipulation of key transcription factors known to directly control photosynthetic machinery can be an effective strategy to improve photosynthetic traits.In this study,we identified an Arabidopsis gain-of-function mutant,cogwheel1-3D,that shows a significantly enlarged rosette and increased biomass compared with wild-type plants.Overexpression of COG1,a Dof transcription factor,recapitulated the phenotype of cogwheel1-3D,whereas knocking out COG1 and its six paralogs resulted in a reduced rosette size and decreased biomass.Transcriptomic and quantitative reverse transcription polymerase chain reaction analyses demonstrated that COG1 and its paralogs were required for light-induced expression of genes involved in photosynthesis.Further chromatin immunoprecipitation and electrophoretic mobility shift assays indicated that COG1 can directly bind to the promoter regions of multiple genes encoding light-harvesting antenna proteins.Physiological,biochemical,and microscopy analyses revealed that COG1 enhances photosynthetic capacity and starch accumulation in Arabidopsis rosette leaves.Furthermore,combined results of bioinformatic,genetic,and molecular experiments suggested that the functions of COG1 in increasing biomass are conserved in different plant species.These results collectively demonstrated that COG1 acts as a key regulator of plant biomass by promoting photosynthesis and starch accumulation.Manipulating COG1 to optimize photosynthetic capacity would create new strategies for future crop yield improvement.