A novel mitochondrial orf147 causes cytoplasmic male sterility in pigeonpea by modulating aberrant anther dehiscence
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A novel open reading frame (ORF) identified and cloned from the A4 cytoplasm of Cajanus cajanifolius induced partial to complete male sterility when introduced into Arabidopsis and tobacco.
Pigeonpea (Cajanus cajan L. Millsp.) is the only legume known to have commercial hybrid seed technology based on cytoplasmic male sterility (CMS). We identified a novel ORF (orf147) from the A4 cytoplasm of C. cajanifolius that was created via rearrangements in the CMS line and co-transcribes with the known and unknown sequences. The bi/poly-cistronic transcripts cause gain-of-function variants in the mitochondrial genome of CMS pigeonpea lines having distinct processing mechanisms and transcription start sites. In presence of orf147, significant repression of Escherichia coli growth indicated its toxicity to the host cells and induced partial to complete male sterility in transgenic progenies of Arabidopsis thaliana and Nicotiana tabacum where phenotype co-segregated with the transgene. The male sterile plants showed aberrant floral development and reduced lignin content in the anthers. Gene expression studies in male sterile pigeonpea, Arabidopsis and tobacco plants confirmed down-regulation of several anther biogenesis genes and key genes involved in monolignol biosynthesis, indicative of regulation of retrograde signaling. Besides providing evidence for the involvement of orf147 in pigeonpea CMS, this study provides valuable insights into its function. Cytotoxicity and aberrant programmed cell death induced by orf147 could be important for mechanism underlying male sterility that offers opportunities for possible translation for these findings for exploiting hybrid vigor in other recalcitrant crops as well.
KeywordsArabidopsis Cajanus cajan Cytoplasmic male sterility Hybrid vigor Pigeonpea Tobacco
This work was undertaken as part of the CGIAR Research Program on Grain Legumes. Thanks to Rahul Nitnavare, Chavvi Srivastava, Divya and Kedarinath for their technical assistance with the transformation and gene expression studies and PS Rao for photography. Critical reviews of the manuscript by Drs. Gopalan Selvaraj, Rajeev Gupta and Damaris Odeny are gratefully acknowledged.
PBM and KKS conceptualized, designed and analyzed all experimental data. RG conducted expression studies in prokaryotic system, Sequence analysis was done by PSR, BPR assisted in cloning and transformation; DSR was involved in qPCR and Northern blot studies. RKS provided inputs on mitochondrial genomic sequence information and analysis. CVSK provided pigeonpea seed material. PBM and KKS conducted histochemical studies. PBM, KKS, RG and PSR contributed to manuscript preparation.
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Conflict of interest
The authors declare no conflict of interest. PBM, RG and KKS are inventors on the patent applications of this work and are current employees of ICRISAT who owns the IP.
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