Polycomb Gene Regulation in Rice Endosperm Development and Global Analysis of Protein Acetylation in Rice
Nallamilli, Babi Ramesh Reddy
Willard, Scott T.
Cereal endosperm represents half of all human food calories and serves as the primary feedstock for livestock. The regulatory mechanism of cereal endosperm development is largely unknown. Polycomb complex has been shown to play a key role in the regulation of endosperm development in Arabidopsis, but its role in cereal endosperm development remains obscure. In addition, the enzyme activities of all the plant polycomb complexes have not been demonstrated in vitro. Here we purified the rice OsFIE2-polycomb complex using tandem affinity purification and demonstrated its specific H3 methyltransferase activity. We found that the OsFIE2 gene product was responsible for H3K27me3 production specifically in vivo and the gene expression was not regulated by imprinting. Genetic studies showed that a severe reduction of OsFIE2 expression led to completely endosperm-free seeds and a moderated reduction of OsFIE2 expression resulted in smaller seeds and loss of seed dormancy. Genome wide ChIP-seq analyses found that a large number of endosperm specific regulatory genes and storage nutrient metabolic pathway genes were directly regulated by H3K27me3 modification in the rice endosperm. Our results suggest that OsFIE2-polycomb complex positively regulates rice endosperm development and grain filling via a mechanism different from that in Arabidopsis. In this dissertation, lysine acetylation, an important posttranslational modification in rice was also studied. Lysine acetylation is a reversible, dynamic protein modification regulated by lysine acetyltransferases and deacetylases. Recent advances in high-throughput proteomics have greatly contributed to the global analysis of lysine acetylation and a large number of proteins of diverse biological function in mammalian and bacterial cells have been shown to be acetylated. However, the extent of lysine acetylation in non-histone proteins remains largely unknown in plants, especially in cereal crops. Here we report a large scale study of lysine acetylation in rice. We identified 112 lysine acetylated sites on 80 proteins with diverse biological functions. Immunoblot studies further validated the presence of a large number of acetylated nonhistone proteins. Overall, our results suggest that lysine acetylation may constitute an important regulatory mechanism for a large number of proteins including both histones and nonhistone proteins.