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 photosynthetic 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 pif 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.

Plant seedlings germinating under the soil are challenged by rough soil grains that can induce physical damage and sudden exposure to light, which can induce photobleaching. Seedlings overcome these challenges by developing apical hooks and by suppressing chlorophyll precursor biosynthesis. These adaptive responses are, respectively, regulated by the phytochrome and ethylene signaling pathways via the PHYTOCHROME-INTERACTING FACTORs (PIFs) and the ETHYLENE INSENSITIVE 3 (EIN3)/EIN3-LIKE transcription factors. Although many processes downstream of phytochrome and ethylene signaling are similar, it remains unclear if and where these pathways converge. Here, we show PIFs and EIN3 induce similar changes in the transcriptome without robustly regulating each other’s signaling pathways. PIFs and EIN3 target highly overlapped gene promoters and activate subsets of the co-target genes either interdependently or additively to induce plant responses. For chlorophyll biosynthesis, PIFs and EIN3 target and interdependently activate the expression of HOOKLESS1. HOOKLESS1, in turn, represses chlorophyll synthesis genes to prevent photobleaching. Thus, our results indicate an integration of the phytochrome and ethylene signaling pathways at the level of transcriptional gene regulation by two core groups of transcription factors, PIFs and EIN3.

Primary standard gas mixtures (PSMs) are typically prepared in cylinders and the amountof-substance fractions are determined by purity analysis and gravimetric method. However, the actual amount-of-substance fraction can be different from the gravimetrically determined value due to adsorption loss onto the internal surface of cylinders. The resulted difference due to the adsorption loss can be larger than the PSM uncertainty. In this study, the cylinderto-cylinder division method is proposed to evaluate any potential physical adsorption loss onto the internal surface of cylinders. A method for estimating the amount of adsorption loss, the corrected amount-of-substance fraction and its uncertainty due to the adsorption loss is described.

Dimethyl sulphide (DMS) plays an important role in atmospheric chemistry and climate change. Ambient DMS is monitored in a global network and reported at sub-nanomole per mole (nmol/mol) levels. Developing traceable, accurate DMS standards at ambient levels is essential for tracking the long-term trends and understanding the role of DMS in the atmosphere. Gravimetrically prepared gas standards in cylinders are widely used for calibrating instruments. Therefore, a stable primary standard gas mixture (PSM) is required for traceable ambient DMS measurement at remote sites. In this study, to evaluate adsorption loss on the internal surface of the gas cylinder, 6 nmol mol−1 DMS gas mixtures were prepared in three types of aluminium cylinders: a cylinder without a special coating on its internal surface (AL), an Aculife IV  +  III-treated cylinder (AC), and an Experis-treated cylinder (EX). There was little adsorption loss on the EX cylinder, whereas there was substantial adsorption loss on the other two cylinders. The EX cylinder was used to prepare 0.5, 2, 5, and 7 nmol mol−1 DMS PSMs with relative expanded uncertainties of less than 0.4%. The DMS PSMs were analytically verified and consistent within a relative expanded uncertainty of less than 1.2%. The long-term stability of the 7 nmol mol−1 DMS PSM was assessed by tracking the ratio of the DMS to the internal standard, benzene. The results showed that the DMS was stable for about seven months and it was projected to be stable for more than 60 months within a relative expanded uncertainty of 3%.