The mitochondrial orf117Sha gene desynchronizes pollen development and causes pollen abortion in Arabidopsis Sha cytoplasmic male sterility.

This article focuses on elucidating the molecular cause and cellular process of pollen abortion in the gametophytic cytoplasmic male sterility (CMS) system known as Sha-CMS in Arabidopsis thaliana. The study confirms that orf117Sha, a mitochondrial gene unique to the Sha cytoplasm, is the causal gene for Sha-CMS by using mitochondrial-targeted transcription activator-like effector nucleases (mitoTALENs) to delete orf117Sha, which restored fertility. In vivo measurements of cytosolic ATP in single pollen grains showed that pollen abortion is not triggered by ATP deficiency; instead, pollen development is desynchronized and pollen death occurs autonomously in individual grains at various developmental stages, preceded by mitochondrial swelling indicative of mitochondrial permeability transition. These findings suggest that mitochondrial morphological changes, rather than energy shortage, underlie pollen death in Sha-CMS, providing new insights into the physiological mechanisms of gametophytic CMS.