OsbZIP76 interacts with OsNF‐YBs and regulates endosperm cellularization in rice (Oryza sativa)

Abstract

Following double fertilization, plant endosperm nuclei undergo syncytial divisions, followed by synchronous cellularization. Cellularization is a key event during endosperm development, but our understanding of its regulation is limited to Arabidopsis. In this study we show that OsbZIP76 regulates cellularization in rice (Oryza sativa). Activation of OsbZIP76 coincided with the initiation of cellularization, and its knockdown or knockout mutants exhibited precocious cellularization. Genes involved in endosperm development or starch biosynthesis were prematurely activated in the osbzip76 caryopsis. As a putative transcription factor, OsbZIP76 alone lacked transcriptional activation activity; however, it interacted with the nuclear factor Y (NF‐Y) family transcription factors OsNF‐YB9 and OsNF‐YB1 in yeast and in planta. OsbZIP76 and OsNF‐YB9 were predominantly expressed in the endosperm and the proteins colocalized. Seeds of osnf‐yb1 and osbzip76 mutants showed reduced size and reduced apparent amylose content. The parent‐of‐origin‐dependent expression of OsbZIP76 is variable in different rice accessions. In summary, OsbZIP76 is an endosperm‐expressed imprinted gene that regulates endosperm development in rice.

Endoplasmic reticulum stress pathway mediates the early heat stress response of developing rice seeds

“…The transcripts of these genes start to accumulate at about 2–3 DAF, which coincides with the coenocytic to cellularization transition stage of endosperm (Chen et al, 2016) (Figures S3 and S6b). Two known endosperm cellularization regulators, OsFIE1 and OsbZIP76 populate this cluster, thus validating the analysis approach for identifying the endosperm enriched heat‐sensitive genes (GSE139445) (Folsom et al, 2014; Niu et al, 2020). Collectively, our PCA‐based analysis integrates several seed dataset and enabled us to identify a small subset of genes that are preferentially expressed in the endosperm and likely regulate its developmental transitions under heat stress.…”

“…Functional elucidation of these endosperm preferential genes could be a promising direction for understanding the heat escape response of rice seeds especially for single seed traits involving yield and quality. These genes include two known rice endosperm regulators, OsFIE1 and OsbZIP76 , which regulate developmental transition from coenocytic to cellular endosperm and seed size (Folsom et al, 2014; Niu et al, 2020). Both overexpression and knock out of OsFIE1 altered the starch quality and produce chalky seeds that weigh less (Dhatt et al, 2021).…”

Starch biosynthesis in cereal endosperms: An updated review over the last decade

“…ZmbZIP91 positively regulates the expression of SSRGs in the maize leaf and endosperm by binding to ACTCAT elements in their promoters ( Chen et al., 2015 ). Knockout or knockdown of OsbZIP76, which regulates endosperm cellularization in rice, caused precocious cellularization in the rice caryopsis and enhanced the expression of SSRGs, leading to earlier starch accumulation ( Niu et al., 2020 ). OsbZIP33/REB/RISBZ2 interacts with GCN4 motifs in the promoters of Wx , SBE1 , and α-globulin genes in rice ( Yang et al., 2001 ; Cai et al., 2002 ).…”

“…A group of nuclear factor Ys (NF-Ys), which are predominantly expressed in the rice endosperm, were also reported to be regulators of rice endosperm development ( Yang et al., 2017 ; Zhiguo et al., 2018 ). Recent findings showed that OsNF-YB1 is specifically expressed in the aleurone layer of the rice developing endosperm and regulates grain filling and endosperm development by interacting with other TFs, including OsbZIP76, OsERF115, OsNF-YC11, OsNF-YC12, and bHLH144 ( Bai et al., 2016 ; Bello et al., 2019 ; Xiong et al., 2019 ; Niu et al., 2020 ). For instance, NF-YB1 binds with NF-YC12 and bHLH144 to form an NF-Y heterotrimer complex (NF-YB1-YC12-bHLH144), and mutation of each gene in the complex can alter starch synthesis in the rice endosperm ( Bello et al., 2019 ).…”

The parent-of-origin lncRNA MISSEN regulates rice endosperm development

“…Endosperm development includes two important processes at early stages, an initial syncytial phase followed by a cellularization phase. Cellularization is critical for endosperm development, and the correct onset of endosperm cellularization could determine the seed size and even seed viability 44 , 45 . Therefore, understanding the molecular mechanisms of endosperm cellularization is important.…”