Pistil-derived lipids influence pollen tube growth and male fertility in Arabidopsis thaliana.

Pollen germination and pollen tube elongation require rapid phospholipid production and remodeling in membrane systems that involve both de novo synthesis and turnover. Phosphatidic acid phosphohydrolase (PAH) and lysophosphatidylcholine acyltransferase (LPCAT) are two key enzymes in membrane lipid maintenance. PAH generates diacylglycerol (DAG), a necessary precursor for the de novo synthesis of phosphatidylcholine (PC), while LPCAT reacylates lysophosphatidylcholine (LPC) to PC and plays an essential role in the remodeling of membrane lipids. In this study, we investigated the synthetic defects of pah and lpcat mutations in sexual reproduction of Arabidopsis (Arabidopsis thaliana) and explored the prospect of pistil lipid provision to pollen tube growth. The combined deficiencies of lpcat and pah led to decreased pollen tube growth in the pistil and reduced male transmission. Interestingly, pistils of the lipid mutant dgat1 ameliorated the male transmission deficiencies of pah lpcat pollen. In contrast, pollination with a non-specific phospholipase C (NPC) mutant exacerbated the fertilization impairment of the pah lpcat pollen. Given the importance of DAG in lipid metabolism and its contrasting changes in the dgat1 and npc mutants, we further investigated whether DAG supplement in synthetic media could influence pollen performance. DAG was incorporated into phospholipids of germinating pollen and stimulated pollen tube growth. Our study provides evidence that pistil derived lipids contribute to membrane lipid synthesis in pollen tube growth, a hitherto unknown role in synergistic pollen-pistil interactions.

Spatiotemporal transcriptomics and metabolic profiling provide insights into gene regulatory networks during lentil seed development.

Lentil (Lens culinaris Medik.) is a nutritious legume with seeds rich in protein, minerals and an array of diverse specialized metabolites. The formation of a seed requires regulation and tight coordination of developmental programs to form the embryo, endosperm and seed coat compartments, which determines the structure and composition of mature seed and thus its end-use quality. Understanding the molecular and cellular events and metabolic processes of seed development is essential for improving lentil yield and seed nutritional value. However, such information remains largely unknown, especially at the seed compartment level. In this study, we generated high-resolution spatiotemporal gene expression profiles in lentil embryo, seed coat and whole seeds from fertilization through maturation. Apart from anatomic differences between the embryo and seed coat, comparative transcriptomics and weighted gene co-expression network analysis revealed embryo- and seed coat-specific genes and gene modules predominant in specific tissues and stages, which highlights distinct genetic programming. Furthermore, we investigated the dynamic profiles of flavonoid, isoflavone, phytic acid and saponin in seed compartments across seed development. Coupled with transcriptome data, we identified sets of candidate genes involved in the biosynthesis of these metabolites. The global view of the transcriptional and metabolic changes of lentil seed tissues throughout development provides a valuable resource for dissecting the genetic control of secondary metabolism and development of molecular tools for improving seed nutritional quality.

Genome-wide occupancy of Arabidopsis SWI/SNF chromatin remodeler SPLAYED provides insights into its interplay with its close homolog BRAHMA and Polycomb proteins.

SPLAYED (SYD) is a SWItch/Sucrose Non-Fermentable (SWI/SNF)-type chromatin remodeler identified in Arabidopsis thaliana (Arabidopsis). It is believed to play both redundant and differential roles with its closest homolog BRAHMA (BRM) in diverse plant growth and development processes. To better understand how SYD functions, we profiled the genome-wide occupancy of SYD and its impact on the global transcriptome and trimethylation of histone H3 on lysine 27 (H3K27me3). To map the global occupancy of SYD, we generated a GFP-tagged transgenic line and used it for chromatin immunoprecipitation experiments followed by next-generation sequencing, by which more than 6000 SYD target genes were identified. Through integrating SYD occupancy and transcriptome profiles, we found that SYD preferentially targets to nucleosome-free regions of expressed genes. Further analysis revealed that SYD occupancy peaks exhibit five distinct patterns, which were also shared by BRM and BAF60, a conserved SWI/SNF complex component, indicating the common target sites of these SWI/SNF chromatin remodelers and the functional relevance of such distinct patterns. To investigate the interplay between SYD and Polycomb-group (PcG) proteins, we performed a genome-wide analysis of H3K27me3 in syd-5. We observed both increases and decreases in H3K27me3 levels at a few hundred genes in syd-5 compared to wild type. Our results imply that SYD can act antagonistically or synergistically with PcG at specific genes. Together, our SYD genome-wide occupancy data and the transcriptome and H3K27me3 profiles provide a much-needed resource for dissecting SYD's crucial roles in the regulation of plant growth and development.

Applying a non-GMO breeding approach with an identified natural variation to reduce food allergen Len c3 in Lens culinaris seeds.

Lentils (Lens culinaris) are produced in diverse agroecological regions and are consumed as one of the most important food legumes worldwide. Lentils possess a nutritional profile from a human health perspective that is not only nutrient dense but also offers a better balance between protein and carbohydrates. However, lentil causes food allergy, which has been a significant concern due to increased consumption in parts of the world. Len c3, a non-specific lipid transfer protein (LTP), was identified as one of the allergens in lentil seeds. In this study, we identified an LTP gene Lcu.2RBY.4g013600 that encodes the lentil allergen Len c3. We then focused on gene screening from a collection of natural accessions to search for natural mutations of the Len c3 allergen-encoding gene. A natural lentil line M11 was identified with mutations at LcLTP3b and low accumulation of vicilin through genomic-assisted approaches. Furthermore, we generated a pool of lentil germplasms with LcLTP3b mutation background through crossing the identified lentil plant M11 with two lentil cultivars, CDC Redmoon and CDC Gold. These generated lentil hybrids can be used as a breeding resource targeting at reducing allergen risk in lentil consumption.

Asymmetric gene expression in grain development of reciprocal crosses between tetraploid and hexaploid wheats.

Production of viable progeny from interploid crosses requires precise regulation of gene expression from maternal and paternal chromosomes, yet the transcripts contributed to hybrid seeds from polyploid parent species have rarely been explored. To investigate the genome-wide maternal and paternal contributions to polyploid grain development, we analyzed the transcriptomes of developing embryos, from zygote to maturity, alongside endosperm in two stages of development, using reciprocal crosses between tetraploid and hexaploid wheats. Reciprocal crosses between species with varied levels of ploidy displayed broad impacts on gene expression, including shifts in alternative splicing events in select crosses, as illustrated by active splicing events, enhanced protein synthesis and chromatin remodeling. Homoeologous gene expression was repressed on the univalent D genome in pentaploids, but this suppression was attenuated in crosses with a higher ploidy maternal parent. Imprinted genes were identified in endosperm and early embryo tissues, supporting predominant maternal effects on early embryogenesis. By systematically investigating the complex transcriptional networks in reciprocal-cross hybrids, this study presents a framework for understanding the genomic incompatibility and transcriptome shock that results from interspecific hybridization and uncovers the transcriptional impacts on hybrid seeds created from agriculturally-relevant polyploid species.

Endosperm-Embryo Communications: Recent Advances and Perspectives.

Seed maturation depends on well-coordinated communications between the processes of endosperm and embryo development. The endosperm is considered to be destined to support embryo development and the timing of endosperm cellularization is critical for embryo growth. Recent findings suggest that the endosperm development and the onset of embryo maturation are two independent processes during seed development. Meanwhile, it is lately reported that several mobile regulators originating from the endosperm are needed to ensure proper embryo growth and seed maturation. In this opinion article, we highlight processes on how endosperm communicates with embryo during seed development and discuss some intriguing questions in light of the latest advancements.

LEAFY COTYLEDON1 expression in the endosperm enables embryo maturation in Arabidopsis.

The endosperm provides nutrients and growth regulators to the embryo during seed development. LEAFY COTYLEDON1 (LEC1) has long been known to be essential for embryo maturation. LEC1 is expressed in both the embryo and the endosperm; however, the functional relevance of the endosperm-expressed LEC1 for seed development is unclear. Here, we provide genetic and transgenic evidence demonstrating that endosperm-expressed LEC1 is necessary and sufficient for embryo maturation. We show that endosperm-synthesized LEC1 is capable of orchestrating full seed maturation in the absence of embryo-expressed LEC1. Inversely, without LEC1 expression in the endosperm, embryo development arrests even in the presence of functional LEC1 alleles in the embryo. We further reveal that LEC1 expression in the endosperm begins at the zygote stage and the LEC1 protein is then trafficked to the embryo to activate processes of seed maturation. Our findings thus establish a key role for endosperm in regulating embryo development.

BdHD1, a histone deacetylase of Brachypodium distachyon, interacts with two drought-responsive transcription factors, BdWRKY24 and BdMYB22.

Histone deacetylases (HDACs) play an important role in plant stress response. In Brachypodium distachyon, which is model species for molecular biology research on monocot plants, the histone deacetylase BdHD1, homologous to AtHDAC1 of the RPD3/HDA1 class, functions as a positive regulator in the plant drought stress response. AtHDAC1 has been found to interact with transcription factors to regulate gene expression. However, the drought-responsive transcription factors that interact with BdHD1 have not been identified yet. Previously, we identified BdWRKY24 and BdMYB22 as drought responsive transcription factors in Brachypodium. In this study, we used yeast two-hybrid (Y2 H) and bimolecular fluorescence complementation (BiFC) assays to show that BdHD1 interacts with BdWRKY24 and BdMYB22. Our findings provides a base to investigate BdHD1-transcription factor complexes in the context of drought stress response in Brachypodium.

Brachypodium histone deacetylase BdHD1 positively regulates ABA and drought stress responses.

Despite recent evidence that HDACs are involved in the environmental stress responses of plants, their roles in the abiotic stress responses of monocot plants remain largely unexplored. We investigated a HDAC gene, Bradi3g08060 (BdHD1), in Brachypodium distachyon. The Brachypodium BdHD1-overexpression plants displayed a hypersensitive phenotype to ABA and exhibited better survival under drought conditions. On the other hand, the RNA-interference plants were insensitive to ABA and showed low survival under drought stress. At the genome-wide level, overexpression of BdHD1 led to lower H3K9 acetylation at the transcriptional start sites of 230 genes than in the wild type plants under the drought treatment. We validated our ChIP-Seq data on 10 selected transcription factor genes from the 230 drought-specific genes. These genes exhibited much lower expression in the BdHD1-overexpression plants compared to the wild type plants under drought stress. We further identified an ABA-inducible transcription factor gene BdWRKY24 that was repressed in BdHD1-OE plants, but highly expressed in RNA-interference plants under drought stress. These results indicate that BdHD1 plays a positive role in ABA sensitivity and drought stress tolerance and they provide a link between the role of BdHD1 and the drought stress response at a genome-wide level in Brachypodium.