GAMETOPHYTIC FACTOR 1,Involved in Pre-mRNA Splicing,Is Essential for Megagametogenesis and Embryogenesis in Arabidopsis

RNA biogenesis is essential and vital for accurate expression of genes. It is obvious that cells cannot continue normal metabolism when RNA splicing is interfered with. sgt13018 is such a mutant, with partial loss of function of GAMETOPHYTIC FACTOR 1 （GFA1）; a gene likely involved in RNA biogenesis in Arabidopsis. The mutant is featured in the phenotype of diminished female gametophyte development at stage FG5 and is associated with the arrest of early embryo development in Arabidopsis. Bioinformatics data showed that homologs of gene GFA1 in yeast and human encode putative U5 snRNPspecific proteins required for pre-mRNA splicing. Furthermore, the result of yeast two-hybrid assay indicated that GFA1 physically interacted with AtBrr2 and AtPrp8, the putative U5 snRNP components, of Arabidopsis. This investigation suggests that GFA1 is involved in mRNA biogenesis through interaction with AtBrr2 and AtPrp8 and functions in megagametogenesis and embryogenesis in plant.

Nucleolar histone deacetylases HDT1,HDT2,and HDT3 regulate plant reproductive development

Nucleolus is a membrane-less organelle where ribosomes are assembled, and ribosomal RNAs(r RNAs)transcribed and processed. The assembled ribosomes composed of ribosomal proteins and r RNAs synthesize proteins for cell survival. In plants, the loss of nucleolar ribosomal proteins often causes gametophytically or embryonically lethality. The amount of r RNAs are under stringent regulation according to demand and partially switched off by epigenetic modifications. However, the molecular mechanism for the selective activation or silencing is still unclear, and the transcriptional coordination of r RNAs and ribosomal proteins is also unknown. Here, we report the critical role of three Arabidopsis nucleolar proteins HDT1,HDT2, and HDT3 in fertility and transcription of r DNAs and r RNA processing-related genes through histone acetylation. This study highlights the important roles of transcriptional repression of ribosome biogenesisrelated genes for plant reproductive development.

SLOW WALKER3,Encoding a Putative DEAD-box RNA Helicase,is Essential for Female Gametogenesis in Arabidopsis

RNA helicases are adenosine tri-phosphatases that unwind the secondary structures of RNAs and are required in almost any aspect of RNA metabolism. They are highly conserved from prokaryotic to eukaryotic organisms. However, their precise roles in plant physiology and development remain to be clarified. Here we report that the mutation in the gene SLOW WALKER3 （SWA3） results in the slow and retarded progression of mitosis during megagametogenesis in Arabidopsis. SWA3 is a putative RNA helicase of the DEAD-box subfamily. Mutant megagametophyte development is arrested at fouror eight-nucleate stages, furthermore, one of the synergids in about half of the mutant embryo sacs displays abnormal polarity, with its nucleus locating at the chalazal end, instead of the micropylar end in the wild-type. Transmission of the mutation through female gametophytes is severely reduced in swa3. However, a small portion of mutant embryo sacs are able to develop into mature and functional female gametophytes when pollination was postponed. The SWA3 in Arabidopsis is a homolog of Dbp8 in yeast. Dbp8 interacts with Efs2 and is essential for biogenesis of 18S rRNA in yeast. Our data suggest that SWA3 may form a complex with AtEfs2 and take roles in ribosomal biogenesis as RNA helicase during megagametogenesis in Arabidopsis.

Novel Nuclear Protein ALC-INTERACTING PROTEIN1 is Expressed in Vascular and Mesocarp Cells in Arabidopsis

Pod shattering is an agronomical trait that is a result of the coordinated action of cell differentiation and separation. In Arabidopsis, pod shattering is controlled by a complex genetic network in which ALCATRAZ （ALC）, a member of the basic helix-loop-helix family, is critical for cell separation during fruit dehiscence. Herein, we report the identification of ALC-INTERACTING PROTEIN1 （ACI1） via the yeast two-hybrid screen. ACll encodes a nuclear protein with a lysine-rich domain and a C-terminal serine-rich domain. ACI1 is mainly expressed in the vascular system throughout the plant and mesocarp of the valve in siliques. Our data showed that ACI1 interacts strongly with the N-terminal portion of ALC in yeast cells and in plant cells in the nucleus as demonstrated by bimolecular fluorescence complementaUon assay. Both ACI1 and ALC share an overlapping expression pattern, suggesting that they likely function together in planta. However, no detectable phenotype was found in plants with reduced ACll expression by RNA interference technology, suggesting that ACll may be redundant. Taken together, these data indicate that ALC may interact with ACI1 and its homologs to control cell separation during fruit dehiscence in Arabidopsis.

Erratum to“Nucleolar histone deacetylases HDT1,HDT2,and HDT3 regulate plant reproductive development”[Journal of Genetics and Genomics(2022)49,30–39]

This erratum clarifies information in the article“Nucleolar histone deacetylases HDT1,HDT2,and HDT3 regulate plant reproductive development”by Luo et al.(2021).In the section on“Phenotype of hdt mutants”,the T-DNA insertional knockdown mutant for HDT2(hdt2,salk_1247_A02)should be“Sail_1247_A02”in the main text and Fig.3A.

Patterning the embryo in higher plants:Emerging pathways and challenges

Embryogenesis,which establishes the basic body plan for the post-embryonic organs after stereotyped cell divisions,initiates the first step of the plant life cycle.Studies in the last two decades indicate that embryogenesis is a precisely controlled process,and any defect would result in abnormalities.Here we discuss the recent progresses,with a focus on the cellular pathways governing early embryogenesis in the model species Arabidopsis.