The Cpn20-mediated plastid integrity is essential for growth and female gametophyte development in Arabidopsis.

Plastids' function and integrity require quality control of their proteins, and their failure often leads to impairments in plant growth and development. In most angiosperms, plastids propagation exhibits a maternal inheritance pattern. Despite the identification of mechanisms and events related to embryo sac development, the potential role of plastids in controlling female gametophyte (FG) development remains elusive. To characterize the function of a plastid specific cochaperonin (Cpn20) in Arabidopsis, morphological and histological analyses were conducted, combining genetic and cytological analysis with cell-specific fluorescent labeling detection; RNA sequencing and proteome quantitation were performed. We observed that a weak Cpn20 allele (cpn20-a) showed pleiotropic defects of chlorosis, dwarfism, and delayed flowering, while the knockout cpn20-b allele was lethal with abortive ovules in siliques. The embryo sac with the Cpn20 defect was arrested at the single-cell functional megaspore stage with no observation of plastids. Transcriptome and proteome profiling indicated that Cpn20 malfunction affects chloroplast-involved functions during the vegetative stage, while disturbing proplastid biogenesis and cell division during the reproductive stage. We rationalized that Cpn20 deficiency leads to a failure of plastid integrity and biogenesis. Our results reveal that Cpn20 plays a key role in plant growth and FG development via its indispensable function for plastids.