Genome-wide investigation of pentatricopeptide repeat (PPR) gene family in poplar and their expression analysis in response to biotic and abiotic stresses. Genome-wide investigation of pentatricopeptide repeat (PPR) gene family in poplar and their expression analysis in response to biotic and abiotic stresses

Pentatricopeptide repeat (PPR) proteins, which are characterized by tandem 30-40 amino acid sequence motifs, constitute a large gene family in plants. These known PPR proteins have been identified to play important roles in organellar RNA metabolism and plant development in Arabidopsis and rice. However, functions of PPR genes in woody species remain still largely unknown. Here, we identified and characterized a total of 626 PPR genes containing PPR motifs in the poplar genome. A comprehensive genome-wide analysis of the poplar PPR gene family was performed, including chromosomal location, phylogenetic relationships, gene duplication. Transcriptomic analyses identified that 154 of the PtrPPR genes were induced by biotic and abiotic treatments, including Marssonina brunnea, salicylic acid (SA), methyl jasmonate (MeJA), wounding, cold and salinity. Quantitative RT-PCR analysis further confirmed the expression profiles of 11 PtrPPR genes under different stresses. Our results contribute to a more comprehensive understanding the roles of PPR proteins and provided an insight for improving the stress tolerance in poplar. Overall design: Purpose: The goal of this study is to compare the PPR genes profile in Wild Type with biotic and abiotic treatment of P. trichocarpa. Treatment including M. brunnea, SA and MeJA, wound, low temperature, and salinity. Plant material treatment: Hormone treatments: SA (5 mM in water) and MeJA [1mM in 0.1% (v/v) ethanol] were applied at the different concentrations as 5 ml droplets on each plant. The treated plants were immediately covered with a transparent lid. Fungal inoculation: The leaves were collected after 24 h. Leaves of three-month-old plants were inoculated with M. brunnea f.sp. multigermtubi. Mycelial plugs (6 mm) were placed on excised leaves (at least three leaves for each plant). These leaves were incubated in Petri dishes with humid filter paper in a humid chamber for 3 d. Low temperature stress: The healthy, well-hydrated plants were transferred to a growth chamber at 4°C under the same light and photoperiodic conditions for 1 h. After cold treatment, plants were allowed to recover at 20°C for 1 h. Wounding stress: For the wounding treatment, the young leaves of poplar plants were harvested after being punctured with sterile needles and placed at 20°C for 2 h. Salinity stress: The four-week-old seedlings were subjected to salt stress. Saline treatments had the NaCl concentrations of 100 mM added to full-strength Hoagland’s solution for 2 d. Wild type plant were grown in a greenhouse at 25°C under a 14/10 h light/dark cycle. Additionally, the leaves applied for all stress treatments, pathogen infection, CK and DGE analysis were excised from the second and third internodes.