Project description:Citrus canker caused by Xanthomonas citri subsp. citri (Xcc) is one of the most devastating diseases in citrus industry worldwide. Most citrus cultivars such as sweet orange are susceptible to canker disease. Here, we utilized wild citrus to identify canker-resistant germplasms, and found that Atalantia buxifolia, a primitive (distant-wild) citrus, exhibited remarkable resistance to canker disease. Although the susceptibility gene LATERAL ORGAN BOUNDARIES 1 (LOB1) could also be induced in Atalantia after canker infection, the induction extent was far lower than that in sweet orange. In addition, three of amino acids encoded by transcription factor TFIIAγ in Atalantia (AbTFIIAγ) exhibited difference from those in sweet orange (CsTFIIAγ) which could stabilize the interaction between effector PthA4 and effector binding element (EBE) of LOB1 promoter. The mutation of AbTFIIAγ did not change its interaction with transcription factor binding motifs (TFBs). However, the AbTFIIAγ could hardly support the LOB1 expression induced by the PthA4. In addition, the activity of AbLOB1 promoter was significantly lower than that of CsLOB1 under the induction by PthA4. Our results demonstrate that natural variations of AbTFIIAγ and effector binding element (EBE) in the AbLOB1 promoter are crucial for the canker disease resistance of Atalantia. The natural mutations of AbTFIIAγ gene and AbLOB1 promoter in Atalantia provide candidate targets for improving the resistance to citrus canker disease.
Project description:In this study, we have characterized a putative chloroplast ribosome assembly factor. To elucidate transcriptional responses caused by decreased chloroplast function, we have measured the transcriptome of wild-type and knock-down seedlings.
Project description:The transition of chloroplast function from biogenesis to degeneration upon leaf senescence is critical for a plant’s fitness, as nutrient relocation from leaves to reproductive organs is achieved through this process. The optimal timing of transition should be regulated by tight coordination between chloroplast and nucleus, but the underlying mechanisms remain elusive. Here, we describe the regulatory mechanism of this transition. Chloroplast-Related LONG NONCODING RNA 1 (CHLORELLA1) is highly co-expressed with genes coding for chloroplast functionality during leaf development. Leaves of chlorella exhibit precocious senescence symptoms and a decline in the expression of chloroplast-associated genes, indicating that CHLORELLA1 plays a role in maintaining chloroplast function. Mechanistically, nucleus-encoded CHLORELLA1 transcripts are translocated into the chloroplast and contribute to the assembly of the plastid-encoded RNA polymerase (PEP) complex. At aged leaves, decreased expression of CHLORELLA1 attenuates PEP complex assembly and transcription of photosynthesis genes, possibly triggering leaf senescence. Moreover, CHLORELLA1 is directly activated by GLK1/2, master regulators of chloroplast maintenance. Our study unravels a new layer of the regulation via chloroplast-targeted lncRNA as an anterograde signal in timely decision of leaf senescence.
Project description:We found that thylakoid-anchored protein PBF8 is a key regulator for Photosystem I (PSI) biogenesis. To explore the role of PBF8 in regulating chloroplast gene expression, we performed the RNA-seq to compare the the transcript levels of chloroplast-encoded genes between wild type (Col-0) and pbf8 mutants. To this end, we isolated the total RNA form 12-day-old wild type and pbf8 seedlings grown on the MS medium under long-day conditions (14 h light, 10 h dark) at 22 ºC and with a light intensity of 80 µmol m-2 s-1. The rRNAs were deleted using the Ribo-Zero Kit (Epicentre). The resulting rRNA-depleted RNA was used for preparing the sequencing library with NEBNext Single Cell/Low input library Prep Kit. The libraries were pooled and sequenced on an Illumina Nova 6000 system with 150-bp pair-end reads. Finally, our results show that the transcript accumulation for chloroplast-encoded PSI subunit and assembly factor genes between the wild type (Col-0) and pbf8 samples, suggesting PBF8 may not affect the transcript levels of chloroplast-encoded PSI subunits and assembly factors in chloroplasts.