Abstract
In the life cycle of flowering plants, the sporophytic generation takes up most of the time and plays a dominant role in influencing plant growth and development. The embryo cell and endosperm free nucleus divisions establish the critical initiation phase of early sporophyte development, which forms mature seeds through a series of cell growth and differentiation events. Here, we report on the biological functions of two Arabidopsis (Arabidopsis thaliana) mitochondrial proteins, TRANSLOCASE OF THE INNER MEMBRANE9 (TIM9) and TIM10. We found that dysfunction of either AtTIM9 or AtTIM10 led to an early sporophyte-lethal phenotype; the embryo and endosperm both arrest division when the embryo proper developed to 16 to 32 cells. The abortion of tim9-1 and tim10 embryos at the 16/32-cell stage was caused by the loss of cell viability and the cessation of division in the embryo proper region, and this inactivation was due to the collapse of the mitochondrial structure and activity. Our characterization of tim9-1 and tim10 showed that mitochondrial membrane permeability increased and that cytochrome c was released from mitochondria into the cytoplasm in the 16/32-cell embryo proper, indicating that mitochondrial dysfunction occurred in the early sporophytic cells, and thus caused the initiation of a necrosis-like programmed cell death, which was further proved by the evidence of reactive oxygen species and DNA fragmentation tests. Consequently, we verified that AtTIM9 and AtTIM10 are nonredundantly essential for maintaining the mitochondrial function of early embryo proper cells and endosperm-free nuclei; these proteins play critically important roles during sporophyte initiation and development in Arabidopsis.
Highlights
In the life cycle of flowering plants, the sporophytic generation takes up most of the time and plays a dominant role in influencing plant growth and development
We dissected maturing siliques from tim9-1/+, tim9-2/+, and tim10/+ plants to analyze the phenotypes of mutants and found that all of them contained a proportion of aborted white seeds (Fig. 1B, arrows)
The values were close to the expected value of 25%, reconfirming that mutations of AtTIM9 and AtTIM10 led to homozygous progeny lethality
Summary
In the life cycle of flowering plants, the sporophytic generation takes up most of the time and plays a dominant role in influencing plant growth and development. We verified that AtTIM9 and AtTIM10 are nonredundantly essential for maintaining the mitochondrial function of early embryo proper cells and endosperm-free nuclei; these proteins play critically important roles during sporophyte initiation and development in Arabidopsis. Mitochondria play roles in a variety of fundamental and essential functions during the plant life cycle, including early sporophyte development. This has been confirmed through the identification of mitochondrial proteins with specific roles during Arabidopsis embryo and endosperm division (Millar et al, 2008; Hsu et al, 2010; Law et al, 2012). To date, little is known about the importance of TIM10 during Arabidopsis development, neither the relationship between AtTIM9 and AtTIM10 nor the potential functional roles of them in early sporophyte growth
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