The Pentatricopeptide Repeat Protein PGR3 Is Required for the Translation of petL and ndhG by Binding Their 5' UTRs

PGR3 is a P-class pentatricopeptide repeat (PPR) protein required for the stabilization of petL operon RNA and the translation of the petL gene in plastids. Irrespective of its important roles in plastids, key questions have remained unanswered, including how PGR3 protein promotes translation and which plastid mRNA PGR3 activates the translation. Here, we show that PGR3 facilitates the translation from ndhG, in addition to petL, through binding to their 5' untranslated regions (UTRs). Ribosome profiling and RNA sequencing in pgr3 mutants revealed that translation from petL and ndhG was specifically suppressed. Harnessing small RNA fragments protected by PPR proteins in vivo, we probed the PGR3 recruitment to the 5' UTRs of petL and ndhG. The putative PGR3-bound RNA segments per se repress the translation possibly with a strong secondary structure and thereby block ribosomes' access. However, the PGR3 binding antagonizes the effects and facilitates the protein synthesis from petL and ndhG in vitro. The prediction of the 3-dimensional structure of PGR3 suggests that the 26th PPR motif plays important roles in target RNA binding. Our data show the specificity of a plastidic RNA-binding protein and provide a mechanistic insight into translational control.

Overexpression of differentially expressed AhCytb6 gene during plant-microbe interaction improves tolerance to N2 deficit and salt stress in transgenic tobacco

Stenotrophomonas maltophilia has plant growth-promoting potential, and interaction with Arachis hypogaea changes host-plant physiology, biochemistry, and metabolomics, which provides tolerance under the N2 starvation conditions. About 226 suppression subtractive hybridization clones were obtained from plant-microbe interaction, of which, about 62% of gene sequences were uncharacterized, whereas 23% of sequences were involved in photosynthesis. An uncharacterized SSH clone, SM409 (full-length sequence showed resemblance with Cytb6), showed about 4-fold upregulation during the interaction was transformed to tobacco for functional validation. Overexpression of the AhCytb6 gene enhanced the seed germination efficiency and plant growth under N2 deficit and salt stress conditions compared to wild-type and vector control plants. Results confirmed that transgenic lines maintained high photosynthesis and protected plants from reactive oxygen species buildup during stress conditions. Microarray-based whole-transcript expression of host plants showed that out of 272,410 genes, 8704 and 24,409 genes were significantly (p < 0.05) differentially expressed (> 2 up or down-regulated) under N2 starvation and salt stress conditions, respectively. The differentially expressed genes belonged to different regulatory pathways. Overall, results suggested that overexpression of AhCytb6 regulates the expression of various genes to enhance plant growth under N2 deficit and abiotic stress conditions by modulating plant physiology.