Ubiquitin-proteasome pathway plays an essential regulatory role during spermatangium formation in Neopyropia yezoensis

Abstract

Gerproductive cell formation is one of the most important physiological processes of organisms. The Rhodophyta, Neopyropia yezoensis, is a typical Archaeplastida and the spermatangia is usually formed along the edge of thalli and visible to the naked eye. It is therefore meaningful to invest the mechanisms of cell development. Here, the cell clumps at four typical differentiation stages of spermatangium in N. yezoensis were collected and transcriptome analysis was performed. A total of 12,188 differentially expressed genes (DEGs) were identified and the number of DEGs increased compared to the control as spermatangium formation progressed. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that carbon fixation, glycolysis/gluconeogenesis, photosynthesis-antenna proteins and some primary metabolic processes were down-regulated. In contrast, sphingolipid metabolism, inositol phosphate metabolism, ubiquitin mediated proteolysis and DNA replication were up-regulated. The development of spermatangia is believed to be induced by the sex signaling molecules due to the up-regulation of sphingolipid metabolism, the biosynthesis of phytosterol and the expression of a steroid bound receptor of heme-binding b5-domain containing protein at the initial stage of spermatangia formation. During the course of development, a total of 163 DEGs related to the ubiquitin-proteasome (Ub-proteasome) system were identified and half of these were up-regulated. Additionally, a series of ubiquitin-protein ligases (E3s) related to development, cell cycle, and chromosome replication were analyzed by qRT-PCR. The continuously upregulated of histone H2A/H2B implied that the shift of global gene expression profile modulated by the Ub-proteasome system was necessary during the differentiation. The up-regulation of the anaphase-promoting complex (APC) and its related protein factors meant that ubiquitin-mediated proteolysis enhanced the cell-cycle and chromosome replication. All the results suggest that the development of male germ cells is a highly modulated process and the Ub-proteasome system might play an essential regulatory role.