Plasmodesmata (PDs) play vital roles in cell-to-cell communication and plant development. Emerging evidence suggests that sterols are involved in PD activity during cytokinesis. However, whether sterols contribute to PD gating between established cells remains unknown. Here, we isolated GhSCP2D, a putative sterol carrier protein gene from elongating cotton (Gossypium hirsutum) fibers. In contrast to wild-type fiber PDs, which opened at 5-10 days post anthesis (DPA) and closed only at 15-25 DPA, plants with suppressed GhSCP2D expression had reduced sterol contents and closed PDs at 5 through 25 DPA. The GhSCP2D-suppressed fibers exhibited callose deposition at the PDs, likely due to reduced expression of GhPdBG3-2A/D, which encodes a PD-targeting β-1,3-glucanase. Both GhPdBG3-2A/D expression and callose deposition were sensitive to a sterol biosynthesis inhibitor. Moreover, suppressing GhSCP2D upregulated a cohort of SUT and SWEET sucrose transporter genes in fiber cells. Collectively, our results indicate that (i) GhSCP2D is required for GhPdBG3-2A/D expression to degrade callose at the PD, thereby contributing to the establishment of the symplasmic pathway, and (ii) blocking the symplasmic pathway by downregulating GhSCP2D activates or increases the expression of SUTs and SWEETs, leading to the switch from symplasmic to apoplasmic pathways.

Floral organ identities in plants are specified by the combinatorial action of homeotic master regulatory transcription factors. How these factors achieve their regulatory specificities is however still largely unclear. Genome-wide in vivo DNA binding data show that homeotic MADS-domain proteins recognize partly distinct genomic regions, suggesting that DNA binding specificity contributes to functional differences of homeotic protein complexes. We used in vitro systematic evolution of ligands by exponential enrichment followed by high throughput DNA sequencing (SELEX-seq) on several floral MADS-domain protein homo- and heterodimers to measure their DNA-binding specificities. We show that specification of reproductive organs is associated with distinct binding preferences of a complex formed by SEPALLATA3 (SEP3) and AGAMOUS (AG). Binding specificity is further modulated by different binding site spacing preferences. Combination of SELEX-seq and genome-wide DNA binding data allows to differentiate between targets in specification of reproductive versus perianth organs in the flower. We validate the importance of DNA-binding specificity for organ-specific gene regulation by modulating promoter activity through targeted mutagenesis. Our study shows that intrafamily protein interactions affect DNA-binding specificity of floral MADS-domain proteins. Differential DNA-binding of MADS-domain protein complexes plays a role in the specificity of target gene regulatio

Identifying interspecies changes in gene regulation, one of the two primary sources of phenotypic variation, is challenging on a genome-wide scale. The use of paired time course data on cold-responsive gene expression in maize (Zea mays) and sorghum (Sorghum bicolor) allowed us to identify differentially regulated orthologs. While the majority of cold-responsive transcriptional regulation of conserved gene pairs is species specific, the initial transcriptional responses to cold appear to be more conserved than later responses. In maize, the promoters of genes with conserved transcriptional responses to cold tend to contain more micrococcal nuclease hypersensitive sites in their promoters, a proxy for open chromatin. Genes with conserved patterns of transcriptional regulation between the two species show lower ratios of nonsynonymous to synonymous substitutions. Genes involved in lipid metabolism, known to be involved in cold acclimation, tended to show consistent regulation in both species. Genes with species-specific cold responses did not cluster in particular pathways nor were they enriched in particular functional categories. We propose that cold-responsive transcriptional regulation in individual species may not be a reliable marker for function, while a core set of genes involved in perceiving and responding to cold stress are subject to functionally constrained cold-responsive regulation across the grass tribe Andropogoneae.

Alkenes are linear hydrocarbons with one or more double bonds. Despite their potential as biofuels and precursors for specialty chemicals, the underlying biochemistry and genetics of alkene biosynthesis in plants remain elusive. Here, we report on a screen of natural accessions of poplar (Populus trichocarpa) revealing that the leaf cuticular waxes are predominantly composed of alkanes and alkenes. Interestingly, the accumulation of alkenes increases with leaf development, is limited to the abaxial side of the leaf, and is impaired in a few accessions. Among other genes, a β-ketoacyl CoA synthase gene (PotriKCS1) was downregulated in leaves from non-alkene-producing accessions. We demonstrated biochemically that PotriKCS1 elongates monounsaturated fatty acids and is responsible for the recruitment of unsaturated substrates to the cuticular wax. Moreover, we found significant associations between the presence of alkenes and tree growth and resistance to leaf spot. These findings highlight the crucial role of cuticular waxes as the first point of contact with the environment, and they provide a foundation for engineering long-chain monounsaturated oils in other species.

Rapid recovery gene downregulation during excess-light stress and recovery in Arabidopsis

Peter Alexander Crisp, Diep Ganguly, Aaron B Smith, Kevin D Murray, Gonzalo M Estavillo, Iain R Searle, Ethan Ford, Ozren Bogdanović, Ryan Lister, Justin O. Borevitz, Steven R Eichten, and Barry J Pogson

Plant Cell 2017 tpc.16.00828; Advance Publication July 13, 2017; doi:10.1105/tpc.16.00828 OPEN

ZHOUPI and KERBEROS Mediate Embryo/Endosperm Separation by Promoting the Formation of an Extra-Cuticular Sheath at the Embryo Eurface.

Steven A Moussu, Nicolas M. Doll, Sophy Chamot, Lysiane Brocard, Audrey Creff, Chloé Fourquin, Thomas WIDIEZ, Zachary L. Nimchuk, and Gwyneth C. Ingram

Plant Cell 2017 tpc.17.00016; Advance Publication July 10, 2017; doi:10.1105/tpc.17.00016

Homologs of PROTEIN TARGETING TO STARCH Control Starch Granule Initiation in Arabidopsis Leaves

David Seung, Julien Boudet, Jonathan D. Monroe, Tina B Schreier, Laure C. David, Melanie Abt, Kuan-Jen Lu, Martina Zanella, and Samuel C. Zeeman

Plant Cell 2017 tpc.17.00222; Advance Publication July 6, 2017; doi:10.1105/tpc.17.00222 OPEN

ATRX controls H3.3 incorporation in Arabidopsis

AspWood: High-spatial-resolution transcriptome profiles reveal uncharacterized modularity of wood formation in Populus tremula

David Sundell, Nathaniel R Street, Manoj Kumar, Ewa J Mellerowicz, Melis Kucukoglu, Christoffer Johnsson, Vikash Kumar, Chanaka Mannapperuma, Nicolas Delhomme, Ove Nilsson, Hannele Tuominen, Edouard Pesquet, Urs Fischer, Totte Niittylä, Bjorn Sundberg, and Torgeir R Hvidsten

Plant Cell 2017 tpc.17.00153; Advance Publication June 27, 2017; doi:10.1105/tpc.17.00153 OPEN

Spatiotemporal monitoring of Pseudomonas effectors via type III secretion using split fluorescent protein fragments

Eunsook Park, Hye-Young Lee, Jongchan Woo, Doil Choi, and Savithramma P. Dinesh-Kumar

Plant Cell 2017 tpc.17.00047; Advance Publication June 14, 2017; doi:10.1105/tpc.17.00047 OPEN

Secrets of the Forest: Volatiles First Discovered in Pine Trees Propagate Defense Signals Within and Between Plants

Kathleen L Farquharson

Plant Cell 2017 tpc.17.00462; Advance Publication June 13, 2017; doi:10.1105/tpc.17.00462 OPEN

During gravitropism, the directional signal of gravity is perceived by gravity-sensing cells called statocytes, leading to asymmetric distribution of auxin in the responding organs. To identify the genes involved in gravity signaling in statocytes, we performed transcriptome analyses of statocyte-deficient Arabidopsis thaliana mutants and found two candidates from the LAZY1 family, AtLAZY1/LAZY1-LIKE1 (LZY1) and AtDRO3/AtNGR1/LZY2. We showed that LZY1, LZY2, and a paralog AtDRO1/AtNGR2/LZY3 are redundantly involved in gravitropism of the inflorescence stem, hypocotyl, and root. Mutations of LZY genes affected early processes in gravity signal transduction without affecting amyloplast sedimentation. Statocyte-specific expression of LZY genes rescued the mutant phenotype, suggesting that LZY genes mediate gravity signaling in statocytes downstream of amyloplast displacement, leading to the generation of asymmetric auxin distribution in gravity-responding organs. We also found that lzy mutations reversed the growth angle of lateral branches and roots. Moreover, expression of the conserved C-terminal region of LZY proteins also reversed the growth direction of primary roots in the lzy mutant background. In lateral root tips of lzy multiple mutants, asymmetric distribution of PIN3 and auxin response were reversed, suggesting that LZY genes regulate the direction of polar auxin transport in response to gravity through the control of asymmetric PIN3 expression in the root cap columella.

Relationship between BIF and ACT domains - Letter and response http://www.plantcell.org/content/early/2017/07/26/tpc.17.00356 & http://www.plantcell.org/content/early/2017/07/26/tpc.17.00547

Potassium and nitrogen are essential macronutrients for plant growth and have a positive impact on crop yield. Previous studies have indicated that the absorption and translocation of K+ and NO3- are correlated with each other in plants; however, the molecular mechanism that coordinates K+ and NO3- transport remains unknown. In this study, using a forward genetic approach, we isolated a low-K+-sensitive Arabidopsis mutant lks2 that showed a leaf-chlorosis phenotype under low-K+ conditions. LKS2 encodes the transporter NRT1.5/NPF7.3, a member of the NRT1/PTR (Nitrate Transporter 1/Peptide Transporter) family. The lks2/nrt1.5 mutants exhibit a remarkable defect in both K+ and NO3- translocation from root to shoot, especially under low-K+ conditions. The present study demonstrates that LKS2 (NRT1.5) functions as a proton-coupled H+/K+ antiporter. Proton gradient can promote NRT1.5-mediated K+ release out of root parenchyma cells and facilitate K+ loading into the xylem. This study reveals that NRT1.5 plays a crucial role in K+ translocation from root to shoot, and is also involved in the coordination of K+/NO3- distribution in plants.

Lignification of cell wall appositions is a conserved basal defense mechanism in the plant innate immune response. However, the genetic pathway controlling defense-induced lignification remains unknown. Here, we demonstrate the Arabidopsis thaliana SG2-type R2R3-MYB transcription factor MYB15 as a regulator of defense-induced lignification and basal immunity. Loss of MYB15 reduces the content but not the composition of defense-induced lignin, whereas constitutive expression of MYB15 increases lignin content independently of immune activation. Comparative transcriptional and metabolomics analyses implicate MYB15 as necessary for the defense-induced synthesis of guaiacyl lignin and the basal synthesis of the coumarin metabolite scopoletin. MYB15 directly binds to the secondary wall MYB-responsive element consensus sequence, which encompasses the AC elements, to drive lignification. The myb15 and lignin biosynthetic mutants show increased susceptibility to the bacterial pathogen Pseudomonas syringae, consistent with defense-induced lignin having a major role in basal immunity. A scopoletin biosynthetic mutant also shows increased susceptibility independently of immune activation, consistent with a role in preformed defense. Our results support a role for phenylalanine-derived small molecules in preformed and inducible Arabidopsis defense, a role previously dominated by tryptophan-derived small molecules. Understanding the regulatory network linking lignin biosynthesis to plant growth and defense will help lignin engineering efforts to improve the production of biofuels and aromatic industrial products as well as increase disease resistance in energy and agricultural crops.

The hormone jasmonate (JA), which functions in plant immunity, regulates resistance to pathogen infection and insect attack through triggering genome-wide transcriptional reprogramming in plants. We show that the basic helix-loop-helix transcription factor (TF) MYC2 in tomato (Solanum lycopersicum) acts downstream of the JA receptor to orchestrate JA-mediated activation of both the wounding and pathogen responses. Using chromatin immunoprecipitation sequencing (ChIP-seq) coupled with RNA sequencing (RNA-seq) assays, we identified 655 MYC2-targeted JA-responsive genes. These genes are highly enriched in Gene Ontology categories related to TFs and the early response to JA, indicating that MYC2 functions at a high hierarchical level to regulate JA-mediated gene transcription. We also identified a group of MYC2-targeted TFs (MTFs) that may directly regulate the JA-induced transcription of late defense genes. Our findings suggest that MYC2 and its downstream MTFs form a hierarchical transcriptional cascade during JA-mediated plant immunity that initiates and amplifies transcriptional output. As proof of concept, we showed that during plant resistance to the necrotrophic pathogen Botrytis cinerea, MYC2 and the MTF JA2-Like (JA2L) form a transcription module that preferentially regulates wounding-responsive genes, whereas MYC2 and the MTF ETHYLENE RESPONSE FACTOR.C3 (ERF.C3) form a transcription module that preferentially regulates pathogen-responsive genes.

Tracking the Bacterial Type III Secretion System: Visualization of Effector Delivery Using Split Fluorescent Proteins

Jennifer Mach

Plant Cell 2017 tpc.17.00553; Advance Publication July 13, 2017; doi:10.1105/tpc.17.00553 OPEN

MEICA 1 (meiotic chromosome association 1) interacts with TOP3α and regulates meiotic recombination in rice

Qing Hu, Yafei Li, Hongjun Wang, Yi Shen, Chao Zhang, Guijie Du, Ding Tang, and Zhukuan Cheng

New Suppressors of the Chloroplast Protein Import Mutant tic40 Reveal a Genetic Link between Protein Import and Thylakoid Biogenesis

Jocelyn Bédard, Raphael Trösch, Feijie wu, Qihua Ling, Úrsula Flores-Pérez, Mats Töpel, Fahim Nawaz, and Paul Jarvis

Plant Cell 2017 tpc.16.00962; Advance Publication July 6, 2017; doi:10.1105/tpc.16.00962 OPEN

A lipid-anchored NAC transcription factor translocates into nucleus to activate GlyI gene expression involved in drought stress

Tao Wang, Jiangli Dong, Rongxue Zhang, Fugui Zhu, Zhenqian Zhang, Lanming Gou, Jiangqi Wen, and Mei Duan

Plant Cell 2017 tpc.17.00044; Advance Publication July 6, 2017; doi:10.1105/tpc.17.00044 OPEN

A Plastid Phosphatidylglycerol Lipase Contributes to the Export of Acyl Groups from Plastids for Seed Oil Biosynthesis

Polyprenols are Synthesized by a Plastidial cis-Prenyltransferase and Influence Photosynthetic Performance

Tariq A Akhtar, Przemysław Surowiecki, Hanna Siekierska, Magdalena Kania, Kristen Van Gelder, Kevin Rea, Lilia Virta, Maritza Vatta, Katarzyna Gawarecka, Jacek Wojcik, Witold Danikiewicz, Daniel Buszewicz, Ewa Swiezewska, and Liliana Surmacz

Plant Cell 2017 tpc.16.00796; Advance Publication June 27, 2017; doi:10.1105/tpc.16.00796 OPEN

CONSTANS Companion: CO Binds the NF-YB/NF-YC Dimer and Confers Sequence-Specific DNA Binding

Jennifer Mach

Plant Cell 2017 tpc.17.00465; Advance Publication June 13, 2017; doi:10.1105/tpc.17.00465 OPEN