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1. The SvFUL2 transcription factor is required for inflorescence determinacy and timely flowering in Setaria viridis

   https://doi.org/10.1093/plphys/kiab169  

   Yang, Jiani; Bertolini, Edoardo; Braud, Max; Preciado, Jesus; Chepote, Adriana; Jiang, Hui; Eveland, Andrea L (April 2021, Plant Physiology)

   null (Ed.)

   Abstract Inflorescence architecture in cereal crops directly impacts yield potential through regulation of seed number and harvesting ability. Extensive architectural diversity found in inflorescences of grass species is due to spatial and temporal activity and determinacy of meristems, which control the number and arrangement of branches and flowers, and underlie plasticity. Timing of the floral transition is also intimately associated with inflorescence development and architecture, yet little is known about the intersecting pathways and how they are rewired during development. Here, we show that a single mutation in a gene encoding an AP1/FUL-like MADS-box transcription factor significantly delays flowering time and disrupts multiple levels of meristem determinacy in panicles of the C4 model panicoid grass, Setaria viridis. Previous reports of AP1/FUL-like genes in cereals have revealed extensive functional redundancy, and in panicoid grasses, no associated inflorescence phenotypes have been described. In S. viridis, perturbation of SvFul2, both through chemical mutagenesis and gene editing, converted a normally determinate inflorescence habit to an indeterminate one, and also repressed determinacy in axillary branch and floral meristems. Our analysis of gene networks connected to disruption of SvFul2 identified regulatory hubs at the intersection of floral transition and inflorescence determinacy, providing insights into the optimization of cereal crop architecture. 

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2. Exploring Grass Morphology & Mutant Phenotypes Using Setaria viridis

   https://doi.org/10.1525/abt.2021.83.5.311  

   Kaggwa, Ruth J.; Jiang, Hui; Ryan, Rita A.; Zahller, Justin Paul; Kellogg, Elizabeth A.; Woodford-Thomas, Terry; Callis-Duehl, Kristine (May 2021, The American Biology Teacher)

   null (Ed.)

   Globally, most human caloric intake is from crops that belong to the grass family (Poaceae), including sugarcane (Saccharum spp.), rice (Oryza sativa), maize (or corn, Zea mays), and wheat (Triticum aestivum). The grasses have a unique morphology and inflorescence architecture, and some have also evolved an uncommon photosynthesis pathway that confers drought and heat tolerance, the C4 pathway. Most secondary-level students are unaware of the global value of these crops and are unfamiliar with plant science fundamentals such as grass architecture and the genetic concepts of genotype and phenotype. Green foxtail millet (Setaria viridis) is a model organism for C4 plants and a close relative of globally important grasses, including sugarcane. It is ideal for teaching about grass morphology, the economic value of grasses, and the C4 photosynthetic pathway. This article details a teaching module that uses S. viridis to engage entire classrooms of students in authentic research through a laboratory investigation of grass morphology, growth cycle, and genetics. This module includes protocols and assignments to guide students through the process of growing one generation of S. viridis mutants and reference wild-type plants from seed to seed, taking measurements, making critical observations of mutant phenotypes, and discussing their physiological implications. 

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3. Maize ANT1 modulates vascular development, chloroplast development, photosynthesis, and plant growth

   https://doi.org/10.1073/pnas.2012245117  

   Liu, Wen-Yu; Lin, Hsin-Hung; Yu, Chun-Ping; Chang, Chao-Kang; Chen, Hsiang-June; Lin, Jinn-Jy; Lu, Mei-Yeh Jade; Tu, Shih-Long; Shiu, Shin-Han; Wu, Shu-Hsing; et al (September 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   Arabidopsis AINTEGUMENTA (ANT), an AP2 transcription factor, is known to control plant growth and floral organogenesis. In this study, our transcriptome analysis and in situ hybridization assays of maize embryonic leaves suggested that maize ANT1 (ZmANT1) regulates vascular development. To better understand ANT1 functions, we determined the binding motif of ZmANT1 and then showed that ZmANT1 binds the promoters of millet SCR1 , GNC , and AN3 , which are key regulators of Kranz anatomy, chloroplast development, and plant growth, respectively. We generated a mutant with a single-codon deletion and two frameshift mutants of the ANT1 ortholog in the C4 millet Setaria viridis by the CRISPR/Cas9 technique. The two frameshift mutants displayed reduced photosynthesis efficiency and growth rate, smaller leaves, and lower grain yields than wild-type (WT) plants. Moreover, their leaves sporadically exhibited distorted Kranz anatomy and vein spacing. Conducting transcriptomic analysis of developing leaves in the WT and the three mutants we identified differentially expressed genes (DEGs) in the two frameshift mutant lines and found many down-regulated DEGs enriched in photosynthesis, heme, tetrapyrrole binding, and antioxidant activity. In addition, we predicted many target genes of ZmANT1 and chose 13 of them to confirm binding of ZmANT1 to their promoters. Based on the above observations, we proposed a model for ANT1 regulation of cell proliferation and leaf growth, vascular and vein development, chloroplast development, and photosynthesis through its target genes. Our study revealed biological roles of ANT1 in several developmental processes beyond its known roles in plant growth and floral organogenesis. 

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4. WUSCHEL- dependent chromatin regulation in maize inflorescence development at single-cell resolution

   https://doi.org/10.1101/2024.05.13.593957  

   Bang, Sohyun; Zhang, Xuan; Gregory, Jason; Chen, Zongliang; Galli, Mary; Gallavotti, Andrea; Schmitz, Robert J (May 2024, bioRxiv)

   SUMMARY WUSCHEL (WUS) is transcription factor vital for stem cell proliferation in plant meristems. In maize,ZmWUS1is expressed in the inflorescence meristem, including the central zone, the reservoir of stem cells.ZmWUS1overexpression in theBarren inflorescence3mutant leads to defects in inflorescence development. Here, single-cell ATAC-seq analysis shows thatZmWUS1overexpression alters chromatin accessibility throughout the central zone. The CAATAATGC motif, a known homeodomain recognition site, is predominantly observed in the regions with increased chromatin accessibility suggesting ZmWUS1 is an activator in the central zone. Regions with decreased chromatin accessibility feature various motifs and are adjacent toAUXIN RESPONSE FACTORgenes, revealing negative regulation of auxin signaling in the central zone. DAP-seq of ZmWUS1 identified the TGAATGAA motif, abundant in epidermal accessible chromatin compared to the central zone. These findings highlight ZmWUS1’s context-dependent mechanisms for stem cell maintenance in the inflorescence meristem. 

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5. Cantil: a previously unreported organ in wild-type Arabidopsis regulated by FT, ERECTA and heterotrimeric G proteins

   https://doi.org/10.1242/dev.195545  

   Gookin, Timothy E.; Assmann, Sarah M. (June 2021, Development)

   null (Ed.)

   ABSTRACT We describe a previously unreported macroscopic Arabidopsis organ, the cantil, named for its ‘cantilever’ function of holding the pedicel at a distance from the stem. Cantil development is strongest at the first nodes after the vegetative to reproductive inflorescence transition; cantil magnitude and frequency decrease acropetally. Cantils develop in wild-type Arabidopsis accessions (e.g. Col-0, Ws and Di-G) as a consequence of delayed flowering in short days; cantil formation is observed in long days when flowering is delayed by null mutation of the floral regulator FLOWERING LOCUS T. The receptor-like kinase ERECTA is a global positive regulator of cantil formation; therefore, cantils never form in the Arabidopsis strain Ler. ERECTA functions genetically upstream of heterotrimeric G proteins. Cantil expressivity is repressed by the specific heterotrimeric complex subunits GPA1, AGB1 and AGG3, which also play independent roles: GPA1 suppresses distal spurs at cantil termini, while AGB1 and AGG3 suppress ectopic epidermal rippling. These G protein mutant traits are recapitulated in long-day flowering gpa1-3 ft-10 plants, demonstrating that cantils, spurs and ectopic rippling occur as a function of delayed phase transition, rather than as a function of photoperiod per se. 

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