The processed C-terminus of AvrRps4 effector suppresses plant immunity via targeting multiple WRKYs

Pathogens generate and secrete effector proteins to the host plant cells during pathogenesis to promote virulence and colonization.If the plant carries resistance(R)proteins that recognize pathogen effectors,effector-triggered immunity(ETI)is activated,resulting in a robust immune response and hypersensitive response(HR).The bipartite effector AvrRps4 from Pseudomonas syringae pv.pisi has been well studied in terms of avirulence function.In planta,AvrRps4 is processed into two parts.The Cterminal fragment of AvrRps4(AvrRps4^(C))induces HR in turnip and is recognized by the paired resistance proteins AtRRS1/AtRPS4 in Arabidopsis.Here,we show that AvrRps4^(C)targets a group of Arabidopsis WRKY,including WRKY46,WRKY53,WRKY54,and WRKY70,to induce its virulence function.Indeed,AvrRps4^(C)suppresses the general binding and transcriptional activities of immune-positive regulator WRKY54 and WRKY54-mediated resistance.AvrRps4^(C)interferes with WRKY54's binding activity to target gene SARD1 in vitro,suggesting WRKY54 is sequestered from the SARD1 promoter by AvrRps4^(C).Through the interaction of Avr Rps4^(C)with four WRKYs,AvrRps4 enhances the formation of homo-/heterotypic complexes of four WRKYs and sequesters them in the cytoplasm,thus inhibiting their function in plant immunity.Together,our results provide a detailed virulence mechanism of AvrRps4 through its C-terminus.

Whole-Plant Live Imaging of Reactive Oxygen Species

Reactive oxygen species(ROS)are key regulators of numerous subcellular,cellular,and systemic signals.They function in plants as an integral part of many different hormonal,physiological,and developmental pathways,as well as play a critical role in defense and acclimation responses to different biotic and abiotic conditions.Although many ROS imaging techniques have been developed and utilized in plants,a wholeplant imaging platform for the dynamic detection of ROS in mature plants is lacking.Here we report a robust and straightforward method for the whole-plant live imaging of ROS in mature plants grown in soil.This new method could be used to study local and systemic ROS signals in different genetic variants,conduct phenotyping studies to identify new pathways for ROS signaling,monitor the stress level of different plants and mutants,and unravel novel routes of ROS integration into stress,growth regulation,and development in plants.We demonstrate the utility of this new method for studying systemic ROS signals in different A rabidopsis mutants and wound responses in cereals such as wheat and corn.

SWEET as Sugar： New Sucrose Effluxers in Plants

Photosynthesis leads to the fixation of carbon in leaves and to the accumulation of carbohydrates （e.g., sucrose, starch）. This assimilated carbon must be transported from the leaves （source tissues） to non-photosynthetic organs （sink tissues）, such as roots and seeds. Despite the essentiality of this process in plants, a complete understanding of the actors involved in sucrose export from leaves is lacking. SWEET proteins are a newly identified class of sugar transporters that facilitate dif- fusion of sugars across cell membranes down a concentration gradient. In this perspective, we highlight the recent publica- tion of Chen et al. （2012）, which reports that SWEET proteins transport sucrose across cell membranes, are expressed in a subset of phloem parenchyma cells,

Single-cell transcriptome atlases of soybean root and mature nodule reveal new regulatory programs that control the nodulation process

The soybean root system is complex.In addition to being composed of various cell types,the soybean root system includes the primary root,the lateral roots,and the nodule,an organ in which mutualistic symbiosis with N-fixing rhizobia occurs.A mature soybean root nodule is characterized by a central infection zone where atmospheric nitrogen is fixed and assimilated by the symbiont,resulting from the close cooperation between the plant cell and the bacteria.To date,the transcriptome of individual cells isolated from developing soybean nodules has been established,but the transcriptomic signatures of cells from the mature soybean nodule have not yet been characterized.Using single-nucleus RNA-seq and Molecular Cartography technologies,we precisely characterized the transcriptomic signature of soybean root and mature nodule cell types and revealed the co-existence of different sub-populations of B.diazoefficiens-infected cells in the mature soybean nodule,including those actively involved in nitrogen fixation and those engaged in senescence.Mining of the single-cell-resolution nodule transcriptome atlas and the associated gene co-expression network confirmed the role of known nodulation-related genes and identified new genes that control the nodulation process.For instance,we functionally characterized the role of GmFWL3,a plasma membrane microdomain-associated protein that controls rhizobial infection.Our study reveals the unique cellular complexity of the mature soybean nodule and helps redefine the concept of cell types when considering the infection zone of the soybean nodule.

The barren stalk2 Gene Is Required for Axillary Meristem Development in Maize

The diversity of plant architecture is determined by axillary meristems (AMs). AMs are produced from small groups of stem cells in the axils of leaf primordia and generate vegetative branches and reproductive inflorescences . Previous studies identified genes critical for AM development that function in auxin biosynthesis, transport, and signaling. barren stalkl (ba1), a basic helix-loop-helix transcription factor, acts downstream of auxin to control AM formation. Here, we report the cloning and characterization of barren stalk2 (ba2), a mutant that fails to produce ears and has fewer branches and spikelets in the tassel, indicating that ba2 functions in reproductive AM development. Furthermore, the ba2 mutation suppresses tiller growth in the teosinte branchedl mutant, indicating that ba2 also plays an essential role in vegetative AM development. The ba2 gene encodes a protein that co-localizes and heterodimerizes with BA1 in the nucleus . Characterization of the genetic interaction between ba2 and ba1 demonstrates that ba1 shows a gene dosage effect in ba2 mutants, providing further evidence that BA1 and BA2 act together in the same pathway. Characterization of the molecular and genetic interaction between ba2 and additional genes required for the regulation of ba1 further supports this finding. The ba1 and ba2 genes are orthologs of rice genes, LAX PANICLE1 (LAX1) and LAX2, respectively, hence providing insights into pathways controlling AMs development in grasses.

Letting Go is Never Easy:Abscission and Receptor- Like Protein Kinases

Abscission is the process by which plants discard organs in response to environmental cues/stressors, or as part of their normal development. Abscission has been studied throughout the history of the plant sciences and in numerous species. Although long studied at the anatomical and physiological levels, abscission has only been elucidated at the molecular and genetic levels within the last two decades, primarily with the use of the model plant Arabidopsis thaliana. This has led to the discovery of numerous genes involved at all steps of abscission, including key pathways involving receptor-like protein kinases （RLKs）. This review covers the current knowledge of abscission research, highlighting the role of RLKs.

Sucrose transporter2 contributes to maize growth,development,and crop yield

During daylight, plants produce excess photo- synthates, including sucrose, which is temporarily stored in the vacuole. At night, plants remobilize sucrose to sustain metabolism and growth. Based on homology to other sucrose transporter （SUT） proteins, we hypothesized the maize （Zea mays） SUCROSE TRANSPORTER2 （ZmSUT2） protein functions as a sucrose/H^＋ symporter on the vacuolar membrane to export transiently stored sucrose. To understand the biological role of ZmSut2, we examined its spatial and temporal gene expression, determined the protein subcellular localization, and characterized loss-of- function mutations. ZmSut2 mRNA was ubiquitously expressed and exhibited diurnal cycling in transcript abundance. Expressing a translational fusion of ZmSUT2 fused to a red fluorescent protein in maize mesophyll cell protoplasts revealed that the protein localized to the tonoplast. Under field conditions, zmsut2 mutant plants grew slower, possessed smaller tassels and ears, and produced fewer kernels when compared to wild-type siblings, zmsut2 mutants also accumulated two-fold more sucrose, glucose, and fructose as well as starch in source leaves compared to wild type. These findings suggest （i） ZmSUT2 functions to remobilize sucrose out of the vacuole for subsequent use in growing tissues; and （ii） its function provides an important contribution to maize development and agronomic yield.

Auxin EvoDevo: Conservation and Diversification of Genes Regulating Auxin Biosynthesis, Transport, and Signaling

The phytohormone auxin has been shown to be of pivotal importance in growth and development of land plants.The underlying molecular players involved in auxin biosynthesis, transport, and signaling are quite well understood in Arabidopsis.However, functional characterizations of auxin-related genes in economically important crops, specifically maize and rice, are still limited.In this article, we comprehensively review recent functional studies on auxirelated genes in both maize and rice, compared with what is known in Arabidopsis, and highlight conservation and diversification of their functions. Our analysis is illustrated by phylogenetic analysis and publicly available gene expression data for each gene family, which will aid in the identification of auxin-related genes for future research.Current challenges and future directions for auxin research in maize and rice are discussed.Developments in gene editing techniques provide powerful tools for overcoming the issue of redundancy in these gene families and will undoubtedly advance auxin research in crops.

Maize Carbohydrate Partitioning Defective33 Encodes an MCTP Protein and Functions in Sucrose Export from Leaves

To sustain plant growth,development,and crop yield,sucrose must be transported from leaves to distant parts of the plant,such as seeds and roots.To identify genes that regulate sucrose accumulation and transport in maize(Zea mays),we isolated carbo/iydrafe part/f/ofi/ngf defecf/Ve33(cpd33),a recessive mutant that accumulated excess starch and soluble sugars in mature leaves.The cpd33 mutants also exhibited chlorosis in the leaf blades,greatly diminished plant growth,and reduced fertility.Cpd33 encodes a protein containing multiple C2 domains and transmembrane regions.Subcellular localization experiments showed the CPD33 protein localized to plasmodesmata(PD),the plasma membrane,and the endoplasmic reticulum.We also found that a loss-of-function mutant of the CPD33 homolog in Arabidopsis,QUIRKY,had a similar carbohydrate hyperaccumulation phenotype.Radioactively labeled sucrose transport assays showed that sucrose export was significantly lower in cpd33 mutant leaves relative to wild-type leaves.However,PD transport in the adaxial-abaxial direction was unaffected in cpd33 mutant leaves.Intriguingly,transmission electron microscopy revealed fewer PD at the companion cell-sieve element interface in mutant phloem tissue,providing a possible explanation for the reduced sucrose export in mutant leaves.Collectively,our results suggest that CPD33 functions to promote symplastic transport into sieve elements.

Regulation of Ethylene Biosynthesis and Signaling by Protein Kinases and Phosphatases

Ethylene, a gaseous plant hormone, plays critical roles in plant growth, development, and response to environment. Ethylene-regulated processes are initiated by the elevation of ethylene biosynthesis, which is under tight control by a complex signaling network. An elevated level of ethyl- ene is then perceived by ethylene receptors in local and neighboring cells, which activates signaling pathways that lead to ethylene responses. Different types of tissues/cells have differential capacities in producing ethylene and dif- ferential sensitivity to ethylene, which are crucial to the diverse functions of ethylene in plants. This report high- lights recent advances in our understanding of kinases and phosphatases in ethylene biosynthesis and signaling.

New microsome-associated HT-family proteins from Nicotiana respond to pollination and define an HT/NOD-24 protein family

HT-family proteins have been identified in Nicotiana, Solanum, and Petunia. HT-B-type proteins are implicated in S-RNase-based self-incompatibility, but the functions of other family members are unknown. Screening for cDNA sequences with an expression pattern similar to HT-B in Nicotiana alata revealed a new group of small HT-family proteins, designated HT-M. HT-M proteins resemble HT-B in several respects： their pistil-specific expression pattern is indistinguishable from HT-B, they pellet with a microsome fraction, and their abundance decreases after pollination. Unlike HT-B, there is no S-specificity to this response, and RNAi experiments show that HT-M proteins are not necessary for self-incompatibility. Identification of a third group of pistil-specific HT-family proteins helps better define the characteristics of the family and allowed identification of putative new family members. By searching the databases with only the most conserved HT- family sequence elements, the signal sequence and cysteine motifs, we identified nodulin-24-1ike proteins and several small glycine-rich proteins as putative HT-family members. Like HT-M and HT-B, nodulin-24 is membrane associated. We propose that the conserved features in HT-family proteins are important for targeting or modification and refer to the broader family that includes both HT- and nodulin-24-1ike proteins as the HT/NOD-24-family.

Primary metabolism:It’s more than what's for dinner

At the risk of oversimplifying,plant–pathogen interactions are a battle for nutrients in the form of primary metabolic intermediates.Plants have them.Pathogens want them.Sugars,amino acids,and organic acids are continuously being exported from source cells to supply both other plant cells and potentially beneficial microorganisms(Kim et al.,2021).Logically,plants attempt to restrict access to pathogens by withholding these nutrients upon infection;and successful pathogens have evolved strategies to restore nutrient availability(Kim et al.,2021).