Rose is one of the most important ornamental crops worldwide and powdery mildew (Podosphaera pannosa (Wallr.: Fr.) de Bary) is the major disease of rose when grown in polyhouse or open field. Understanding of plant–pathogen interaction is important to develop strategies for disease management. We profiled transcriptomes of powdery mildew‐resistant rose line IIHRR13‐4 and susceptible cultivar Konfetti using Illumina NGS platform to understand the molecular mechanism of resistance to powdery mildew in the rose line IIHRR13‐4. Profiles of samples were collected at 0 hr after inoculation (hai), 36 hai and 72 hai from susceptible cultivar Konfetti (SCON0, SCON3 and SCON7) and 0 hai and 36 hai from resistant line IIHRR13‐4 (RPMR0 and RPMR3). The high‐quality reads were aligned to reference genome of Rosa chinensis. The transcripts of rose‐powdery mildew interaction were analysed for functions and involvement in disease resistance. Expression of receptor‐like kinases, putative disease resistance genes (RLKs, NBS‐LRR, NB‐ARC, RPP13), WRKY transcription factors and PR proteins was observed in the transcripts library and was found up‐regulated in IIHRR13‐4 samples. Differentially expressed genes coding for metabolic and cellular process, response to abiotic stress response, defence response and other biosynthetic processes were identified in the transcripts. Gene ontology term enrichment and pathway analysis revealed that transcriptome of IIHRR13‐4 was enriched with transcripts coding for plant hormone signal transduction and plant–pathogen interaction compared to transcripts of susceptible cultivar Konfetti. The transcriptome profiling proved that different defence mechanisms including hypersensitive responses were elicited as systemic acquired resistance in rose line IIHRR13‐4 when infected by powdery mildew pathogen.
Resistance is the best strategy to manage powdery mildew (Podosphaera pannosa (Wallr.:Fr.) de Bary) of rose. Identification of resistant genes (R genes) from plant species will help in breeding programs. Nucleotide Binding Site - Leucine Rich Repeats (NBS- LRR) is a major class of R gene family in plants. This study reports the identification and molecular characterization of resistance gene analogues from roses maintained at ICAR- Indian Institute of Horticultural Research (IIHR). The powdery mildew resistant line IIHRR13-4 was compared with the susceptible commercial cultivar, konfetti. PCR based approaches with degenerative primers based on different conserved motifs of NBS-LRR were employed to isolate resistance gene analogues (RGAs) from rose. Eleven RGAs (IIHRR13-4R1, IIHRR13-4R2, IIHRR13-4R3, IIHRR13-4R4, IIHRR13-4R5, IIHRR13- 4R6, IIHRR13-4R7, IIHRR13-4R8 IIHRR13-4R9 and IIHRR13-4R10) were identified from powdery mildew resistant germplasm line, IIHRR13-4, based on the sequence and similarity to RGAs from rosaceae family and other crops. The major similarity to rose RGAs reported are from Fragaria vesca, Rosa hybrid cultivar, Prunus and Rosa chinensis. RGAs isolated from IIHRR13-4 belonged to Toll Interleukin Receptor (TIR)-NBS-LRR and Non-TIR-NBS-LRR RGAs (Lecine Zipper (LZ) type). Different motifs of RGAs identified were P-loop, RNBS A, kinase 2, kinase 3a, RNBS-D and GLPL of NBS domain. This study reports the existence of resistance at genetic level in powdery mildew resistant genotype IIHRR13-4. These RGAs will be useful for mapping and characterization of R genes in IIHRR13-4 and breeding for improved powdery mildew resistance in roses.
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