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Summary: Seed longevity, the maintenance of viability during dry storage, is a crucial factor to preserve plant genetic resources and seed vigor. Inference of a temporal gene‐regulatory network of seed maturation identified auxin signaling as a putative mechanism to induce longevity‐related genes.Using auxin‐response sensors and tryptophan‐dependent auxin biosynthesis mutants of Arabidopsis thaliana L., the role of auxin signaling in longevity was studied during seed maturation.DII and DR5 sensors demonstrated that, concomitant with the acquisition of longevity, auxin signaling input and output increased and underwent a spatiotemporal redistribution, spreading throughout the embryo. Longevity of seeds of single auxin biosynthesis mutants with altered auxin signaling activity was affected in a dose–response manner depending on the level of auxin activity. Longevity‐associated genes with promoters enriched in auxin response elements and the master regulator ABSCISIC ACID INSENSITIVE3 were induced by auxin in developing embryos and deregulated in auxin biosynthesis mutants. The beneficial effect of exogenous auxin during seed maturation on seed longevity was abolished in abi3‐1 mutants.These data suggest a role for auxin signaling activity in the acquisition of longevity during seed maturation. [ABSTRACT FROM AUTHOR]

Desiccation tolerance (DT) is the capacity to withstand total loss of cellular water. It is acquired during seed filling and lost just after germination. However, in many species, a germinated seed can regain DT under adverse conditions such as osmotic stress. The genes, proteins and metabolites that are required to establish this DT is referred to as the desiccome. It includes both a range of protective mechanisms and underlying regulatory pathways that remain poorly understood. As a first step toward the identification of the seed desiccome of Medicago truncatula, using updated microarrays we characterized the overlapping transcriptomes associated with acquisition of DT in developing seeds and the re-establishment of DT in germinated seeds using a polyethylene glycol treatment (-1.7 MPa). The resulting list contained 740 and 2829 transcripts whose levels, respectively, increased and decreased with DT. Fourty-eight transcription factors (TF) were identified including MtABI3, MtABI5 and many genes regulating flowering transition and cell identity. A promoter enrichment analysis revealed a strong over-representation of ABRE elements together with light-responsive cis-acting elements. In Mtabi5 Tnt1 insertion mutants, DT could no longer be re-established by an osmotic stress. Transcriptome analysis on Mtabi5 radicles during osmotic stress revealed that 13 and 15% of the up-regulated and down-regulated genes, respectively, are mis-regulated in the mutants and might be putative downstream targets of MtABI5 implicated in the re-establishment of DT. Likewise, transcriptome comparisons of the desiccation sensitive Mtabi3 mutants and hairy roots ectopically expressing MtABI3 revealed that 35 and 23% of the up-regulated and down-regulated genes are acting downstream of MtABI3. Our data suggest that ABI3 and ABI5 have complementary roles in DT. Whether DT evolved by co-opting existing pathways regulating flowering and cellular phase transition and cell identity is discussed. [ABSTRACT FROM AUTHOR]

In seeds, desiccation tolerance (DT) and the ability to survive the dry state for prolonged periods of time (longevity) are two essential traits for seed quality that are consecutively acquired during maturation. Using transcriptomic and metabolomic profiling together with a conditional-dependent network of global transcription interactions, we dissected the maturation events from the end of seed filling to final maturation drying during the last 3 weeks of seed development in Medicago truncatula. The network revealed distinct coexpression modules related to the acquisition of DT, longevity, and pod abscission. The acquisition of DT and dormancy module was associated with abiotic stress response genes, including late embryogenesis abundant (LEA) genes. The longevity module was enriched in genes involved in RNA processing and translation. Concomitantly, LEA polypeptides accumulated, displaying an 18-d delayed accumulation compared with transcripts. During maturation, gulose and stachyose levels increased and correlated with longevity. A seed-specific network identified known and putative transcriptional regulators of DT, including ABSCISIC ACID-INSENSITIVE3 (MtABI3), MtABI4, MtABI5, and APETALA2/ ETHYLENE RESPONSE ELEMENT BINDING PROTEIN (AtAP2/EREBP) transcription factor as major hubs. These transcriptional activators were highly connected to LEA genes. Longevity genes were highly connected to two MtAP2/EREBP and two basic leucine zipper transcription factors. A heat shock factor was found at the transition of DT and longevity modules, connecting to both gene sets. Gain- and loss-of-function approaches of MtABI3 confirmed 80% of its predicted targets, thereby experimentally validating the network. This study captures the coordinated regulation of seed maturation and identifies distinct regulatory networks underlying the preparation for the dry and quiescent states. [ABSTRACT FROM AUTHOR]

Seeds of Medicago truncatula, a genomic model species for legumes, exhibit physiological and physical dormancy. Here, the factors influencing the germination behaviour of freshly harvested and stored seeds were investigated using several genotypes. Hardseededness is promoted when mature seeds are equilibrated at relative humidities (RH) below 75%. The release of physical dormancy during imbibition was dependent on the initial water content/RH that the seeds were dried to: the drier the seeds, the longer the imbibition time needed to break physical dormancy. The kinetics of physical dormancy release was slower than that of physiological dormancy, making it possible to uncouple both phenomena. Freshly harvested embryos without seed coverings germinated at the same speed as afterripened seeds. The depth of dormancy varied between different M. truncatula genotypes, from more to less dormant: DZA315.16 > A17 (Jemalong) > R108 > DZA45.5. This difference was eliminated by removing the endosperm. Collectively, these observations indicate that the endosperm is likely the main factor in the reduced germination of freshly harvested seeds. White light decreased germination speed of dormant seeds whereas it had no effect on non-dormant seeds. Recently harvested seeds were most dormant at temperatures above 17°C, whereas afterripened seeds germinated over a wider range of temperature. Fluridone could efficiently break dormancy, reinforcing the role of abscisic acid (ABA) synthesis. However, dormancy was not affected by gibberellic acid (100 μM GA3) or nitrate. The particular dormancy features unravelled here for M. truncatula, combined with the available genomic resources, make it a new, useful model for genetic and molecular studies which can complement those developed for Arabidopsis. [ABSTRACT FROM AUTHOR]

Introduction: The production of highly vigorous seeds with high longevity is an important lever to increase crop production efficiency, but its acquisition during seed maturation is strongly influenced by the growth environment., Methods: An association rule learning approach discovered MtABI4, a known longevity regulator, as a gene with transcript levels associated with the environmentally-induced change in longevity. To understand the environmental sensitivity of MtABI4 transcription, Yeast One-Hybrid identified a class I BASIC PENTACYSTEINE (MtBPC1) transcription factor as a putative upstream regulator. Its role in the regulation of MtABI4 was further characterized., Results and Discussion: Overexpression of MtBPC1 led to a modulation of MtABI4 transcripts and its downstream targets. We show that MtBPC1 represses MtABI4 transcription at the early stage of seed development through binding in the CT-rich motif in its promoter region. To achieve this, MtBPC1 interacts with SWINGER, a sub-unit of the PRC2 complex, and Sin3-associated peptide 18, a sub-unit of the Sin3-like deacetylation complex. Consistent with this, developmental and heat stress-induced changes in MtABI4 transcript levels correlated with H3K27me3 and H3ac enrichment in the MtABI4 promoter. Our finding reveals the importance of the combination of histone methylation and histone de-acetylation to silence MtABI4 at the early stage of seed development and during heat stress., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Dang, Lalanne, Ly Vu, Ly Vu, Defaye, Verdier, Leprince and Buitink.)

Seed vigor is an estimate of how successfully a seed lot will establish seedlings under a wide range of environmental conditions, with both the embryo and the surrounding endosperm playing distinct roles in the germination behaviour. Germination and seedling establishment are essential for crop production to be both sustainable and profitable. Seed vigor traits are sequentially acquired during development via genetic programs that are poorly understood, but known to be under the strong influence of environmental conditions. To investigate how light and temperature have an impact on the molecular mechanisms governing seed vigor at harvest, RNA sequencing was performed on Solanum lycopersicum cv. Moneymaker seed tissues (i.e. embryo and endosperm) that were dissected from fruits that were submitted to standard or high temperature and/or standard or dim light. The dataset encompassed a total of 26.5 Gb raw data from mature embryo and endosperm tissues transcriptomes. The raw and mapped reads data on build SL4.0 and annotation ITAG4.0 are available under accession GSE158641 at NCBI Gene Expression Omnibus (GEO) database. Data on seed vigor characteristics are presented together with the differentially expressed gene transcripts. GO and Mapman annotations were generated on ITAG4.0 to analyse this dataset and are provided for datamining future datasets., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships which have or could be perceived to have influenced the work reported in this article., (© 2020 The Authors. Published by Elsevier Inc.)