Female germline development is fundamental to plant reproduction. During megasporogenesis, a somatic ovule cell differentiates into a megaspore mother cell (MMC) and undergoes meiosis to produce a single haploid megaspore while three spores degenerate. The surviving functional megaspore undergoes three rounds of mitosis during the process of megagametogenesis to produce the seven-celled female gametophyte or embryo sac. The mechanism by which the functional megaspore initiates gametogenesis remained unclear. Here, we show that the chromatin remodelling protein SWI3b is required for the initiation of megagametogenesis, but not for megasporogenesis. SWI3b activity either in the MMC or somatic ovule primordium cells alone is not sufficient for the initiation of megagametogenesis. We identified AGO5 as a direct target of SWI3b, which restricts AGO5 expression to the nucellus. We further show that SWI3b is required for maintaining low histone H3 lysine 9 acetylation level at the AGO5 locus, while elevated AGO5 abundance in the nucellus disrupts the initiation of megagametogenesis. In summary, our study reveals that SWI3b promotes the initiation of megagametogenesis through chromatin-mediated repression of AGO5, leading to its exclusion from the MMC and thereby linking histone acetylation and epigenetic mechanisms to the development of the female germ cells. Highlights The chromatin remodeling complex component SWI3b is required for the initiation of megagametogenesis and early embryo development. In ovule primordia SWI3b restricts AGO5 expression to the nucellus SWI3b acts via regulating histone acetylation around the AGO5 transcription start site. Development of female germ cells are associated to histone acetylation
Wen Gong, Liping Liu, H. Cai et al.· bioRxiv· 0 citations
Plant growth and reproduction require coordinated control of hormone-dependent tissue patterning and faithful meiotic chromosome segregation, yet whether upstream proteostasis contributes to both processes remains unclear. Here, we show that Arabidopsis PROTEIN DISULFIDE ISOMERASE 5 (PDI5) contributes to auxin-associated developmental patterning and meiotic fidelity. Native-promoter reporter constructs corresponding to two annotated PDI5 transcript isoforms show distinct subcellular enrichment, with one displaying an endoplasmic reticulum (ER)-associated distribution and the other showing nuclear enrichment. Disruption of PDI5 alters bulk glycoprotein staining and glycoside and trafficking-associated transcriptional programs, reduces the abundance of PIN-FORMED 2-green fluorescent protein (PIN2-GFP), alters its brefeldin A-sensitive intracellular accumulation, and is associated with perturbed auxin-response patterning and disorganized root meristems. In reproductive tissues, the pdi5 mutant shows abnormal germline-associated cell-fate restriction, impaired meiotic chromosome behavior, reduced chiasma formation and decreased fertility. Proteomic and interaction analyses identify the cohesin subunit SISTER-CHROMATID COHESION PROTEIN 3 (SCC3) as a PDI5-associated protein, and disruption of a conserved SCC3 N809-centered motif reduces its detectable association with PDI5. In a PDI5 promoter-driven conditional complementation assay, SCC3^N809E fails to support fertility rescue. These findings support a model in which PDI5-dependent proteostasis contributes to auxin-associated developmental patterning and meiotic chromosome fidelity, potentially through compartmentally distributed PDI5 functions.
M. Aslam, Beenish Fakher, B. H. Jakada et al.· New Phytologist· 0 citations
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