Background: As the final stage of leaf development, leaf senescence may cause the decline of photosynthesis and gradual reduction of carbon assimilation, which makes it a possible limiting factor for crop yield. NACs are plant-specific transcription factors and some NACs have been confirmed to play important roles in regulating leaf senescence. Results: In this study, we reported a member of the NAC transcription factor family named OsNAP whose expression is associated with leaf senescence, and investigated its preliminary function during the process of leaf senescence. The results of qRT-PCR showed that the OsNAP transcripts were accumulated gradually in response to leaf senescence and treatment with methyl jasmonic acid (MeJA). A subcellular localization assay indicated that OsNAP is a nuclear-localized protein. Yeast one-hybrid experiments indicated that OsNAP can bind the NAC recognition site (NACRS)-like sequence. OsNAP-overexpressing transgenic plants displayed an accelerated leaf senescence phenotype at the grain-filling stage, which might be caused by the elevated JA levels and the increased expression of the JA biosynthesis-related genes LOX2 and AOC1, and showed enhanced tolerance ability to MeJA treatment at the seedling stage. Nevertheless, the leaf senescence process was delayed in OsNAP RNAi transgenic plants with a dramatic drop in JA levels and with decreased expression levels of the JA biosynthesis-related genes AOS2, AOC1 and OPR7. Conclusions: These results suggest that OsNAP acts as a positive regulator of leaf senescence and this regulation may occur via the JA pathway.

Summary: Plastid‐encoded genes are coordinately transcribed by the nucleus‐encoded RNA polymerase (NEP) and the plastid‐encoded RNA polymerase (PEP). Resulting primary transcripts are frequently subject to RNA editing by cytidine‐to‐uridine conversions at specific sites. The physiological role of many editing events is largely unknown. Here, we have used the CRISPR/Cas9 technique in rice to knock out a member of the PLS‐DYW subfamily of pentatricopeptide repeat (PPR) proteins. We found that OsPPR16 is responsible for a single editing event at position 545 in the chloroplast rpoB messenger RNA (mRNA), resulting in an amino acid change from serine to leucine in the β‐subunit of the PEP. In striking contrast to loss‐of‐function mutations of the putative orthologue in Arabidopsis , which were reported to have no visible phenotype, knockout of OsPPR16 leads to impaired accumulation of RpoB, reduced expression of PEP‐dependent genes, and a pale phenotype during early plant development. Thus, by editing the rpoB mRNA, OsPPR16 is required for faithful plastid transcription, which in turn is required for Chl synthesis and efficient chloroplast development. Our results provide new insights into the interconnection of the finely tuned regulatory mechanisms that operate at the transcriptional and post‐transcriptional levels of plastid gene expression.

The PPR-SMR protein ATP4 is required for RNA editing of the chloroplast encoded rps8 gene in rice and maize, and the defect in rps8 expression underlies a cold-

As glyphosate is a broad spectrum herbicide extensively used in agriculture worldwide, identification of new aroA genes with high level of glyphosate tolerance is essential for the development and breeding of transgenic glyphosate-tolerant crops. In this study, an aroA gene was cloned from a Janibacter sp. strain isolated from marine sediment (designated as aroA_{J. sp}). The purified aroA_{J. sp} enzyme has a K_m value of 30 μM for PEP and 83 μM for S3P and a significantly higher K_i value for glyphosate (373 μM) than aroA_{E. coli}. AroA_{J. sp} is characterized as a novel and naturally occurring class I aroA enzyme with glyphosate tolerance. Furthermore, we show that aroA_{J. sp} can be used as an effective selectable marker in both japonica and indica rice cultivar. Transgenic rice lines were tested by herbicide bioassay and it was confirmed that they could tolerate up to 3360 g/ha glyphosate, a dosage four-fold that of the recommended agricultural application level. To our knowledge, it is the first report of a naturally occurring novel class I aroA gene which can be efficiently utilized to study and develop transgenic glyphosate-tolerant crops and can facilitate a more economical and simplified weed control system.