The secondary cell wall (SCW) of xylem vessel cells provides rigidity and strength that enables efficient water conduction throughout the plant. To gain insight into SCW deposition, we mutagenized Arabidopsis thaliana VASCULAR-RELATED NAC-DOMAIN7-inducible plant lines, in which ectopic protoxylem vessel cell differentiation is synchronously induced. The baculites mutant was isolated based on the absence of helical SCW patterns in ectopically-induced protoxylem vessel cells, and mature baculites plants exhibited an irregular xylem (irx) mutant phenotype in mature plants. A single nucleic acid substitution in the CELLULOSE SYNTHASE SUBUNIT 7 (CESA7) gene in baculites was identified: while the mutation was predicted to produce a C-terminal truncated protein, immunoblot analysis revealed that cesa7bac mutation results in loss of production of CESA7 proteins, indicating that baculites is a novel cesa7 loss-of-function mutant. In cesa7bac, despite a lack of patterned cellulose deposition, the helically-patterned deposition of other SCW components, such as the hemicellulose xylan and the phenolic polymer lignin, was not affected. Similar phenotypes were found in another point mutation mutant cesa7mur10-2, and an established knock-out mutant, cesa7irx3-4. Taken together, we propose that the spatio-temporal deposition of different SCW components, such as xylan and lignin, is not dependent on cellulose patterning.

/pdf/patterned-deposition-of-xylan-and-lignin-is-independent-from-tafbgh56jx.pdf

Patterned Deposition of Xylan and Lignin is Independent from that of the Secondary Wall Cellulose of Arabidopsis Xylem Vessels.

Source-sink relationships are key to overall crop performance. Detailed understanding of the factors that determine source-sink dynamics is imperative for the balance of biomass and grain yield in crop plants. We investigated the differences in source-sink relationships between a cultivated rice, Oryza sativa cv. Nipponbare, and a wild rice, Oryza australiensis, which show striking differences in biomass and grain yield. Oryza australiensis, which accumulates a higher biomass, not only showed higher photosynthesis per unit leaf area but also exported more sucrose from leaves compared with Nipponbare. However, grain features and sugar content suggested limited sucrose mobilization to grains in the wild rice due to vasculature and sucrose transporter functions. Low cell wall invertase activity and high sucrose synthase cleavage activity followed by higher expression of cellulose synthase genes in O. australiensis stem indicated that it utilized photosynthates preferentially for the synthesis of structural carbohydrates, resulting in high biomass. In contrast, source-sink relationships favored high grain yield in Nipponbare via accumulation of transitory starch in the stem, due to higher expression of starch biosynthetic genes, which is mobilized to panicles at the grain filling stage. Thus, vascular features, sucrose transport, and functions of sugar metabolic enzymes explained the differences in source-sink relationships between Nipponbare and O. australiensis.

Sucrose transport and metabolism control carbon partitioning between stem and grain in rice.

Abstract Many plants accumulate transitory starch reserves in their leaves during the day to buffer their carbohydrate supply against fluctuating light conditions, and to provide carbon and energy for survival at night. It is universally accepted that transitory starch is synthesized from ADP-glucose (ADPG) in the chloroplasts. However, the consensus that ADPG is made in the chloroplasts by ADPG pyrophosphorylase has been challenged by a controversial proposal that ADPG is made primarily in the cytosol, probably by sucrose synthase (SUS), and then imported into the chloroplasts. To resolve this long-standing controversy, we critically re-examined the experimental evidence that appears to conflict with the consensus pathway. We show that when precautions are taken to avoid artefactual changes during leaf sampling, Arabidopsis thaliana mutants that lack SUS activity in mesophyll cells (quadruple sus1234 ) or have no SUS activity (sextuple sus123456 ) have wild-type levels of ADPG and starch, while ADPG is 20 times lower in the pgm and adg1 mutants that are blocked in the consensus chloroplastic pathway of starch synthesis. We conclude that the ADPG needed for starch synthesis in leaves is synthesized primarily by ADPG pyrophosphorylase in the chloroplasts. 

/pdf/sucrose-synthases-are-not-involved-in-starch-synthesis-in-2pzri7mz.pdf

Sucrose synthases are not involved in starch synthesis in Arabidopsis leaves

Gastrodia elata, a fully mycoheterotrophic orchid without photosynthetic ability, only grows symbiotically with the fungus Armillaria The mechanism of carbon distribution in this mycoheterotrophy is unknown We detected high sucrose concentrations in all stages of Gastrodia tubers, suggesting sucrose may be the major sugar transported between fungus and orchid Thick symplasm-isolated wall interfaces in colonized and adjacent large cells implied involvement of sucrose importers Two sucrose transporter (SUT)-like genes, GeSUT4 and GeSUT3, were identified that were highly expressed in young Armillaria-colonized tubers Yeast complementation and isotope tracer experiments confirmed that GeSUT4 functioned as a high-affinity sucrose-specific proton-dependent importer Plasma-membrane/tonoplast localization of GeSUT4-GFP fusions and high RNA expression of GeSUT4 in symbiotic and large cells indicated that GeSUT4 likely functions in active sucrose transport for intercellular allocation and intracellular homeostasis Transgenic Arabidopsis overexpressing GeSUT4 had larger leaves but were sensitive to excess sucrose and roots were colonized with fewer mutualistic Bacillus, supporting the role of GeSUT4 in regulating sugar allocation This is not only the first documented carbon import system in a mycoheterotrophic interaction but also highlights the evolutionary importance of sucrose transporters for regulation of carbon flow in all types of plant-microbe interactions

GeSUT4 mediates sucrose import at the symbiotic interface for carbon allocation of heterotrophic Gastrodia elata (Orchidaceae)

Mild reductions in guard cell sucrose synthase 2 expression leads to slower stomatal opening and decreased whole plant transpiration in Nicotiana tabacum L

Sucrose synthase (SuSy) is one of two enzyme families capable of catalyzing the first degradative step in sucrose utilization. Several earlier studies examining SuSy mutants in Arabidopsis failed to identify obvious phenotypic abnormalities compared with wild-type plants in normal growth environments, and as such a functional role for SuSy in the previously proposed cellulose biosynthetic process remains unclear. Our study systematically evaluated the precise subcellular localization of all six isoforms of Arabidopsis SuSy via live-cell imaging. We showed that yellow fluorescent protein (YFP)-labeled SuSy1 and SuSy4 were expressed exclusively in phloem companion cells, and the sus1/sus4 double mutant accumulated sucrose under hypoxic conditions. SuSy5 and SuSy6 were found to be parietally localized in sieve elements and restricted only to the cytoplasm. SuSy2 was present in the endosperm and embryo of developing seeds, and SuSy3 was localized to the embryo and leaf stomata. No single isoform of SuSy was detected in developing xylem tissue of elongating stem, the primary site of cellulose deposition in plants. SuSy1 and SuSy4 were also undetectable in the protoxylem tracheary elements, which were induced by the vascular-related transcription factor VND7 during secondary cell wall formation. These findings implicate SuSy in the biological events related to sucrose translocation in phloem.

Arabidopsis sucrose synthase localization indicates a primary role in sucrose translocation in phloem

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most destructive foliar diseases of wheat. In this study, we combined the bulked segregant RNA sequencing (BSR-seq) and comparative genomics analysis to localize the powdery mildew resistance gene in Chinese landrace Xiaomaomai. Genetic analysis of F1 plants from a crossing of Xiaomaomai × Lumai23 and the derived F2 population suggests that a single recessive gene, designated as pmXMM, confers the resistance in this germplasm. A genetic linkage map was constructed using the newly developed SNP markers and pmXMM was mapped to the distal end of chromosome 2AL. The two flanking markers 2AL15 and 2AL34 were closely linked to pmXMM at the genetic distance of 3.9 cM and 1.4 cM, respectively. Using the diagnostic primers of Pm4, we confirmed that Xiaomaomai carries a Pm4 allele and the gene function was further validated by the virus-induced gene silencing (VIGS). In addition, we systematically analyzed pmXMM in comparison with the other Pm4 alleles. The results suggest that pmXMM is identical to Pm4d and Pm4e at sequence level. Pm4b is also not different from Pm4c according to their genome/amino acid sequences. Only a few nucleotide variances were detected between pmXMM and Pm4a/b, which indicate the haplotype variation of the Pm4 gene.

https://www.mdpi.com/1422-0067/23/3/1194/pdf?version=1642996632

Identification of a Pm4 Allele as a Powdery Mildew Resistance Gene in Wheat Line Xiaomaomai

Low temperature injury in spring has seriously destabilized the production and grain quality of common wheat. However, the molecular mechanisms underlying spring frost tolerance remain elusive. In this study, we investigated the response of a frost-tolerant wheat variety Zhongmai8444 to freezing stress at the meiotic stage. Transcriptome profiles over a time course were subsequently generated by high-throughput sequencing. Our results revealed that the prolonged freezing temperature led to the significant reductions in plant height and seed setting rate. Cell wall thickening in the vascular tissue was also observed in the stems. RNA-seq analyses demonstrated the identification of 1010 up-regulated and 230 down-regulated genes shared by all time points of freezing treatment. Enrichment analysis revealed that gene activity related to hormone signal transduction and cell wall biosynthesis was significantly modulated under freezing. In addition, among the identified differentially expressed genes, 111 transcription factors belonging to multiple gene families exhibited dynamic expression pattern. This study provided valuable gene resources beneficial for the breeding of wheat varieties with improved spring frost tolerance.

/pdf/transcriptomic-profiling-of-wheat-stem-during-meiosis-in-2p42gn9c.pdf

Transcriptomic profiling of wheat stem during meiosis in response to freezing stress

Simple Summary Tsetse flies are blood-sucking insect vectors belonging to the order Diptera and are widely distributed in the areas of sub-Saharan Africa. These vectors can transmit the pathogenic parasite Trypanosoma brucei (T. brucei) which can cause a disease called African trypanosomiasis. Currently, discovering effective therapeutic drugs and vaccines with minor side effects is still one of the ongoing efforts to treat the disease as well as to prevent the epidemic. Genome technology has recently played an important role in uncovering the molecular mechanisms of many vector-borne diseases, which facilitates the identification of potential drug targets. To better understand the pathological contribution of parasite–host interactions to the disease, we studied the genomic and transcriptomic profiles of T. brucei. We identified a panel of pathogenic proteins and microRNAs supported by their molecular functions in T. brucei for the first time. Our study may pave a new avenue for designing preventive and therapeutic strategies to control this insect vector. Abstract Tsetse flies are a type of blood-sucking insect living in diverse locations in sub-Saharan Africa. These insects can transmit the unicellular parasite Trypanosoma brucei (T. brucei) which causes African trypanosomiasis in mammals. There remain huge unmet needs for prevention, early detection, and effective treatments for this disease. Currently, few studies have investigated the molecular mechanisms of parasite–host interactions underlying African trypanosomiasis, mainly due to a lack of understanding of the T. brucei genome. In this study, we dissected the genomic and transcriptomic profiles of T. brucei by annotating the genome and analyzing the gene expression. We found about 5% of T. brucei proteins in the human proteome, while more than 80% of T. brucei protein in other trypanosomes. Sequence alignment analysis showed that 142 protein homologs were shared among T. brucei and mammalian genomes. We identified several novel proteins with pathogenic potential supported by their molecular functions in T. brucei, including 24 RNA-binding proteins and six variant surface glycoproteins. In addition, 26 novel microRNAs were characterized, among which five miRNAs were not found in the mammalian genomes. Topology analysis of the miRNA-gene network revealed three genes (RPS27A, UBA52 and GAPDH) involved in the regulation of critical pathways related to the development of African trypanosomiasis. In conclusion, our work opens a new door to understanding the parasite–host interaction mechanisms by resolving the genome and transcriptome of T. brucei.

/pdf/genome-wide-screening-for-pathogenic-proteins-and-micrornas-17wvp28b.pdf

Danyu Yao

Papers

Arabidopsis sucrose synthase localization indicates a primary role in sucrose translocation in phloem

Identification of a Pm4 Allele as a Powdery Mildew Resistance Gene in Wheat Line Xiaomaomai

Transcriptomic profiling of wheat stem during meiosis in response to freezing stress

Genome-Wide Screening for Pathogenic Proteins and microRNAs Associated with Parasite–Host Interactions in Trypanosoma brucei