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RETINOBLASTOMA-RELATED ( RBR ) is an essential gene in plants, but its molecular function outside of its role in cell cycle entry remains poorly understood. We characterized the functions of OsRBR1 and OsRBR2 in plant growth and development in rice using both forward- and reverse-genetics methods. The two genes were coexpressed and performed redundant roles in vegetative organs but exhibited separate functions in flowers. OsRBR1 was highly expressed in the floral meristem and regulated the expression of floral homeotic genes to ensure floral organ formation. Mutation of OsRBR1 caused loss of floral meristem identity, resulting in the replacement of lodicules, stamens, and the pistil with either a panicle-like structure or whorls of lemma-like organs. OsRBR2 was preferentially expressed in stamens and promoted pollen formation. Mutation of OsRBR2 led to deformed anthers without pollen. Similar to the protein interaction between AtRBR and AtMSI1 that is essential for floral development in Arabidopsis, OsMSI1 was identified as an interaction partner of OsRBR1 and OsRBR2. OsMSI1 was ubiquitously expressed and appears to be essential for development in rice ( Oryza sativa ), as the mutation of OsMSI1 was lethal. These results suggest that OsRBR1 and OsRBR2 function with OsMSI1 in reproductive development in rice. This work characterizes further functions of RBR s and improves current understanding of specific regulatory pathways of floral specification and pollen formation in rice., (© 2019 American Society of Plant Biologists. All Rights Reserved.)

OsMADS16, a class B floral organ identity gene, plays a pivotal role in stamen formation in rice. To date, little is known about the interacting partners of OsMADS16 except for several MADS-box proteins. In this study, we constructed a high-quality cDNA library of young panicles (< 5 cm in length) and performed yeast two-hybrid (Y2H) screening using OsMADS16 as bait. Eleven candidate proteins interacting with OsMADS16 were identified by Y2H and validated by BiFC and Co-IP assays. Subcellular localization results further confirmed the possibility of the interactions of OsMADS16 with 10 of the candidate proteins in natural rice cells. Bioinformatics analysis indicated that these partners exerted various molecular, cellular and physiological functions. Some of them were known or likely to be related to reproductive events, such as stamen primordium initiation, differentiation and development (OsMADS2, OsMADS4 and OsCOP9) and pollen development (OsbHLH40 and Os6PGDH). Our results provide an important reference for further research on OsMADS16-mediated regulation mechanism on floral organ development and pollen formation., Competing Interests: The authors have declared that no competing interests exist.

Recent studies have shown that F-box proteins constitute a large family in eukaryotes, and play pivotal roles in regulating various developmental processes in plants. However, their functions in monocots are still obscure. In this study, we characterized a recessive mutant dwarf and deformed flower 1-1 (ddf1-1) in Oryza sativa (rice). The mutant is abnormal in both vegetative and reproductive development, with significant size reduction in all organs except the spikelet. DDF1 controls organ size by regulating both cell division and cell expansion. In the ddf1-1 spikelet, the specification of floral organs in whorls 2 and 3 is altered, with most lodicules and stamens being transformed into glume-like organs and pistil-like organs, respectively, but the specification of lemma/palea and pistil in whorls 1 and 4 is not affected. DDF1 encodes an F-box protein anchored in the nucleolus, and is expressed in almost all vegetative and reproductive tissues. Consistent with the mutant floral phenotype, DDF1 positively regulates B-class genes OsMADS4 and OsMADS16, and negatively regulates pistil specification gene DL. In addition, DDF1 also negatively regulates the Arabidopsis LFY ortholog APO2, implying a functional connection between DDF1 and APO2. Collectively, these results revealed that DDF1, as a newly identified F-box gene, is a crucial genetic factor with pleiotropic functions for both vegetative growth and floral organ specification in rice. These findings provide additional insights into the molecular mechanism controlling monocot vegetative and reproductive development., (© 2012 The Authors. The Plant Journal © 2012 Blackwell Publishing Ltd.)

Med8, a subunit of mediator complex, has proved to possess crucial functions in many organisms from yeast to human. In plant, the med8 mutant of Arabidopsis thaliana displayed delayed anthesis and increased number of leaves during the vegetative period. However, the roles of Med8 in other flowering plants are still unknown. To investigate the function of Med8 ortholog in tobacco (Nicotiana tabacum L.; named as NtMed8), we created transgenic tobacco plants with repressed NtMed8 expression mediated by RNA interference (RNAi). Compared with the wild type, the NtMed8-RNAi plants exhibited: more leaves with smaller but thicker blades; larger cells and vascular bundles with lower stomata density in leaves; swelled chloroplasts with thicker and lumen-enlarged thylakoids; weaker root system with fewer lateral roots; larger flowers and floral organs; flowering earlier under long day, but later under short day conditions; and male sterile with larger but less germinable pollens. In addition, quantitative RT-PCR indicated that NtMed8 is expressed in both vegetative and floral tissues. Subcellular localization analysis by transient expression of fusion protein in Nicotiana benthamiana leaves showed that NtMed8 was located in both plasma membrane and nucleus. These results suggest that NtMed8 plays important roles in both vegetative and reproductive development, and the function of Med8 appears to be, at least partially, conserved in flowering plants.

In this article, we report an independent work of positional cloning and functional characterization of OsJAG gene in rice. The merit of our work is that we used a genuine null mutant, in which the wild-type allele was completely deleted. This allowed us to identify the mutant phenotypes accurately without the interference of residual function of the target gene. OsJAG is an important gene with pleiotropy, expressing almost throughout the plant and acting in both vegetative phase and reproductive phase. But its main and crucial roles are in regulating the development of all floral organs, especially in specifying the identity of stamens. Interestingly, OsJAG does not affect the number of floral organ primordial and so of floral organs in each whorl, suggesting that OsJAG does not influence the initiation of floral organ primordia, but affect the developmental fate of all floral organs after their primordia have initiated. Loss of OsJAG function results in maldevelopment of all floral organs, such as degenerated lemma and palea, elongated lodicules and deformed and sterile pistil. The stamen appears to be more sensitive to the mutation. All the six stamens in a mutant floret were thoroughly transformed into six pistil-like organs developed at the presumptive positions of the stamens in whorl 3.