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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)

   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 optimizationmore »of cereal crop architecture.« less
2. Tomato locule number and fruit size controlled by natural alleles of lc and fas

   https://doi.org/10.1002/pld3.142  

   Chu, Yi‐Hsuan ; Jang, Jyan‐Chyun ; Huang, Zejun ; van der Knaap, Esther ( July 2019 , Plant Direct)

   Improving yield by increasing the size of produce is an important selection criterion during the domestication of fruit and vegetable crops. Genes controlling meristem organization and organ formation work in concert to regulate the size of reproductive organs. In tomato,lcandfascontrol locule number, which often leads to enlarged fruits compared to the wild progenitors.LCis encoded by the tomato ortholog ofWUSCHEL(WUS), whereasFASis encoded by the tomato ortholog ofCLAVATA3 (CLV3). The critical role of theWUS‐CLV3 feedback loop in meristem organization has been demonstrated in several plant species. We show that mutant alleles for both loci in tomato led to an expansion of theSlWUSexpression domain in young floral buds 2–3 days after initiation. Single and double mutant alleles oflcandfasmaintain higherSlWUSexpression during the development of the carpel primordia in the floral bud. This augmentation and altered spatial expression ofSlWUSprovided a mechanistic basis for the formation of multilocular and large fruits. Our results indicated thatlcandfasare gain‐of‐function and partially loss‐of‐function alleles, respectively, while both mutations positively affect the size of tomato floral meristems. In addition, expression profiling showed thatlcandfasaffected the expression of several genes in biological processes including those involved in meristem/flower development, patterning, microtubule bindingmore »activity, and sterol biosynthesis. Several differentially expressed genes co‐expressed withSlWUShave been identified, and they are enriched for functions in meristem regulation. Our results provide new insights into the transcriptional regulation of genes that modulate meristem maintenance and floral organ determinacy in tomato.

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3. Pleiotropic and nonredundant effects of an auxin importer in Setaria and maize

   https://doi.org/10.1093/plphys/kiac115  

   Zhu, Chuanmei ; Box, Mathew S ; Thiruppathi, Dhineshkumar ; Hu, Hao ; Yu, Yunqing ; Martin, Callista ; Doust, Andrew N ; McSteen, Paula ; Kellogg, Elizabeth A ( March 2022 , Plant Physiology)

   Abstract Directional transport of auxin is critical for inflorescence and floral development in flowering plants, but the role of auxin influx carriers (AUX1 proteins) has been largely overlooked. Taking advantage of available AUX1 mutants in green millet (Setaria viridis) and maize (Zea mays), we uncover previously unreported aspects of plant development that are affected by auxin influx, including higher order branches in the inflorescence, stigma branch number, glume (floral bract) development, and plant fertility. However, disruption of auxin flux does not affect all parts of the plant, with little obvious effect on inflorescence meristem size, time to flowering, and anther morphology. In double mutant studies in maize, disruptions of ZmAUX1 also affect vegetative development. A green fluorescent protein (GFP)-tagged construct of the Setaria AUX1 protein Sparse Panicle1 (SPP1) under its native promoter showed that SPP1 localizes to the plasma membrane of outer tissue layers in both roots and inflorescences, and accumulates specifically in inflorescence branch meristems, consistent with the mutant phenotype and expected auxin maxima. RNA-seq analysis indicated that most gene expression modules are conserved between mutant and wild-type plants, with only a few hundred genes differentially expressed in spp1 inflorescences. Using clustered regularly interspaced short palindromic repeats (CRISPR)–Cas9 technology,more »we disrupted SPP1 and the other four AUX1 homologs in S. viridis. SPP1 has a larger effect on inflorescence development than the others, although all contribute to plant height, tiller formation, and leaf and root development. The AUX1 importers are thus not fully redundant in S. viridis. Our detailed phenotypic characterization plus a stable GFP-tagged line offer tools for future dissection of the function of auxin influx proteins.« less
4. Genetic control of branching patterns in grass inflorescences

   https://doi.org/10.1093/plcell/koac080  

   Kellogg, Elizabeth A. ( March 2022 , The Plant Cell)

   Inflorescence branching in the grasses controls the number of florets and hence the number of seeds. Recent data on the underlying genetics come primarily from rice and maize, although new data are accumulating in other systems as well. This review focuses on a window in developmental time from the production of primary branches by the inflorescence meristem through to the production of glumes, which indicate the transition to producing a spikelet. Several major developmental regulatory modules appear to be conserved among most or all grasses. Placement and development of primary branches are controlled by conserved auxin regulatory genes. Subtending bracts are repressed by a network including TASSELSHEATH4, and axillary branch meristems are regulated largely by signaling centers that are adjacent to but not within the meristems themselves. Gradients of SQUAMOSA-PROMOTER BINDING-like and APETALA2-like proteins and their microRNA regulators extend along the inflorescence axis and the branches, governing the transition from production of branches to production of spikelets. The relative speed of this transition determines the extent of secondary and higher order branching. This inflorescence regulatory network is modified within individual species, particularly as regards formation of secondary branches. Differences between species are caused both by modifications of gene expressionmore »and regulators and by presence or absence of critical genes. The unified networks described here may provide tools for investigating orphan crops and grasses other than the well-studied maize and rice.

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5. Gene duplication at the Fascicled ear1 locus controls the fate of inflorescence meristem cells in maize

   https://doi.org/10.1073/pnas.2019218118  

   Du, Yanfang ; Lunde, China ; Li, Yunfu ; Jackson, David ; Hake, Sarah ; Zhang, Zuxin ( February 2021 , Proceedings of the National Academy of Sciences)

   Plant meristems are self-renewing groups of pluripotent stem cells that produce lateral organs in a stereotypical pattern. Of interest is how the radially symmetrical meristem produces laminar lateral organs. Both the male and female inflorescence meristems of the dominant Fascicled ear ( Fas1 ) mutant fail to grow as a single point and instead show deep branching. Positional cloning of two independent Fas1 alleles identified an ∼160 kb region containing two floral genes, the MADS-box gene, zmm8 , and the YABBY gene, drooping leaf2 ( drl2 ). Both genes are duplicated within the Fas1 locus and spatiotemporally misexpressed in the mutant inflorescence meristems. Increased zmm8 expression alone does not affect inflorescence development; however, combined misexpression of zmm8 , drl2 , and their syntenic paralogs zmm14 and drl1 , perturbs meristem organization. We hypothesize that misexpression of the floral genes in the inflorescence and their potential interaction cause ectopic activation of a laminar program, thereby disrupting signaling necessary for maintenance of radially symmetrical inflorescence meristems. Consistent with this hypothesis, RNA sequencing and in situ analysis reveal altered expression patterns of genes that define distinct zones of the meristem and developing leaf. Our findings highlight the importance of strict spatiotemporal patterns ofmore »expression for both zmm8 and drl2 and provide an example of phenotypes arising from tandem gene duplications.« less