MutS HOMOLOG1 mediates fertility reversion via ORF220 substoichiometric shifting from cytoplasmic male sterility.

Spontaneous fertility reversion has been documented in cytoplasmic male sterile (CMS) plants of several species, influenced in frequency by nuclear genetic background. In this study, we found that MutS HOMOLOG1 (MSH1) mediates fertility reversion via substoichiometric shifting (SSS) of the CMS-associated mitochondrial Open Reading Frame 220 (ORF220), a process that may be regulated by pollination signaling in Brassica juncea. We show that plants adjust their growth and development in response to unsuccessful pollination. Measurable decrease in MSH1 transcript levels and evidence of ORF220 SSS under non-pollination conditions suggest that this nuclear-mitochondrial interplay influences fertility reversion in CMS plants in response to physiological signals. Suppression of MSH1 expression induced higher frequency substoichiometric shifting in CMS plants than occurs normally. Transcriptional analysis of floral buds under pollination and non-pollination conditions, and the response of MSH1 expression to different sugars, support the hypothesis that carbon flux is involved in the pollination signaling of fertility reversion in CMS plants. Our findings suggest that facultative gynodioecy as a reproductive strategy may incorporate environmentally-responsive genes like MSH1 as an 'on-off' switch for sterility-fertility transition under ecological conditions of reproductive isolation. This article is protected by copyright. All rights reserved.