The Arabidopsis endosperm is a temperature-sensing tissue that implements seed thermoinhibition through phyB.

Seed thermoinhibition, the repression of germination under high temperatures, prevents seedling establishment under potentially fatal conditions. Thermoinhibition is relevant for phenology and agriculture, particularly in a warming globe. The temperature sensing mechanisms and signaling pathways sustaining thermoinhibition are unknown.

The Arabidopsis mature endosperm promotes seedling cuticle formation via release of sulfated peptides.

In Arabidopsis mature seeds, the onset of the embryo-to-seedling transition is nonautonomously controlled, being blocked by endospermic abscisic acid (ABA) release under unfavorable conditions. Whether the mature endosperm governs additional nonautonomous developmental processes during this transition is unknown. Mature embryos have a more permeable cuticle than seedlings, consistent with their endospermic ABA uptake capability.

Embryonic Photosynthesis Affects Post-Germination Plant Growth.

Photosynthesis is the fundamental process fueling plant vegetative growth and development. The progeny of plants relies on maternal photosynthesis, via food reserves in the seed, to supply the necessary energy for seed germination and early seedling establishment. Intriguingly, before seed maturation, Arabidopsis () embryos are also photosynthetically active, the biological significance of which remains poorly understood.

polyamine uptake transporter 2 (put2) and decaying seeds enhance phyA-mediated germination by overcoming PIF1 repression of germination.

Red light promotes germination after activating phytochrome phyB, which destabilizes the germination repressor PIF1. Early upon seed imbibition, canopy light, unfavorable for photosynthesis, represses germination by stabilizing PIF1 after inactivating phyB. Paradoxically, later upon imbibition, canopy light stimulates germination after activating phytochrome phyA.

Non-canonical RNA-directed DNA methylation participates in maternal and environmental control of seed dormancy.

Seed dormancy is an adaptive trait preventing premature germination out of season. In a previous report (Piskurewicz et al., 2016) we showed that dormancy levels are maternally inherited through the preferential maternal allele expression in the seed endosperm of (), a negative regulator of dormancy.

Dormancy-specific imprinting underlies maternal inheritance of seed dormancy in Arabidopsis thaliana.

Mature seed dormancy is a vital plant trait that prevents germination out of season. In , the trait can be maternally regulated but the underlying mechanisms sustaining this regulation, its general occurrence and its biological significance among accessions are poorly understood. Upon seed imbibition, the endosperm is essential to repress the germination of dormant seeds.

Singlet oxygen- and EXECUTER1-mediated signaling is initiated in grana margins and depends on the protease FtsH2.

Formation of singlet oxygen ((1)O2) has been implicated with damaging photosystem II (PSII) that needs to undergo continuous repair to maintain photosynthetic electron transport. In addition to its damaging effect, (1)O2 has also been shown to act as a signal that triggers stress acclimation and an enhanced stress resistance. A signaling role of (1)O2 was first documented in the fluorescent (flu) mutant of Arabidopsis It strictly depends on the chloroplast protein EXECUTER1 (EX1) and happens under nonphotoinhibitory light conditions.

Basic Techniques to Assess Seed Germination Responses to Abiotic Stress in Arabidopsis thaliana.

The model organism Arabidopsis thaliana has been extensively used to unmask the molecular genetic signaling pathways controlling seed germination in plants. In Arabidopsis, the normal seed to seedling developmental transition involves testa rupture soon followed by endosperm rupture, radicle elongation, root hair formation, cotyledon expansion, and greening. Here we detail a number of basic procedures to assess Arabidopsis seed germination in response to different light (red and far-red pulses), temperature (seed thermoinhibition), and water potential (osmotic stress) environmental conditions.

An Endosperm-Associated Cuticle Is Required for Arabidopsis Seed Viability, Dormancy and Early Control of Germination.

Cuticular layers and seeds are prominent plant adaptations to terrestrial life that appeared early and late during plant evolution, respectively. The cuticle is a waterproof film covering plant aerial organs preventing excessive water loss and protecting against biotic and abiotic stresses. Cutin, consisting of crosslinked fatty acid monomers, is the most abundant and studied cuticular component.

Distinctive profiles of small RNA couple inverted repeat-induced post-transcriptional gene silencing with endogenous RNA silencing pathways in Arabidopsis.

The experimental induction of RNA silencing in plants often involves expression of transgenes encoding inverted repeat (IR) sequences to produce abundant dsRNAs that are processed into small RNAs (sRNAs). These sRNAs are key mediators of post-transcriptional gene silencing (PTGS) and determine its specificity. Despite its application in agriculture and broad utility in plant research, the mechanism of IR-PTGS is incompletely understood.

Spatially and genetically distinct control of seed germination by phytochromes A and B.

Phytochromes phyB and phyA mediate a remarkable developmental switch whereby, early upon seed imbibition, canopy light prevents phyB-dependent germination, whereas later on, it stimulates phyA-dependent germination. Using a seed coat bedding assay where the growth of dissected embryos is monitored under the influence of dissected endosperm, allowing combinatorial use of mutant embryos and endosperm, we show that canopy light specifically inactivates phyB activity in the endosperm to override phyA-dependent signaling in the embryo. This interference involves abscisic acid (ABA) release from the endosperm and distinct spatial activities of phytochrome signaling components.

Isolation of genetic material from Arabidopsis seeds.

Here, we describe a series of methods suitable for the reproducible and abundant isolation of total RNA, genomic DNA, and total protein from dry or imbibed Arabidopsis seeds. The resulting material is suitable for most standard molecular biology procedures.

A seed coat bedding assay shows that RGL2-dependent release of abscisic acid by the endosperm controls embryo growth in Arabidopsis dormant seeds.

Seed dormancy is an ecologically important adaptive trait in plants whereby germination is repressed even under favorable germination conditions such as imbibition with water. In Arabidopsis and most plant species, dormancy absolutely requires an unidentified seed coat germination-repressive activity and constitutively higher abscisic acid (ABA) levels upon seed imbibition. The mechanisms underlying these processes and their possible relationship are incompletely understood.

The GA-signaling repressor RGL3 represses testa rupture in response to changes in GA and ABA levels.

We recently reported that the DELLA factor RGL2 represses testa rupture in response to changes in ABA and GA levels. Here, we provide genetic evidence that this observation extends to RGL3, another DELLA factor whose function was not previously characterized. However, RGL3's repressive activity was seen only in an rgl2 genetic background.

Comparative large-scale analysis of interactions between several crop species and the effector repertoires from multiple pathovars of Pseudomonas and Ralstonia.

Bacterial plant pathogens manipulate their hosts by injection of numerous effector proteins into host cells via type III secretion systems. Recognition of these effectors by the host plant leads to the induction of a defense reaction that often culminates in a hypersensitive response manifested as cell death. Genes encoding effector proteins can be exchanged between different strains of bacteria via horizontal transfer, and often individual strains are capable of infecting multiple hosts.

Far-red light inhibits germination through DELLA-dependent stimulation of ABA synthesis and ABI3 activity.

Under the canopy, far-red (FR) light represses seed germination by inactivating phytochrome photoreceptors. This elicits a decrease in gibberellins (GA) levels and an increase in abscisic acid (ABA) levels. GA promotes germination by enhancing the proteasome-mediated destruction of DELLA repressors.

The gibberellic acid signaling repressor RGL2 inhibits Arabidopsis seed germination by stimulating abscisic acid synthesis and ABI5 activity.

Seed germination is antagonistically controlled by the phytohormones gibberellic acid (GA) and abscisic acid (ABA). GA promotes seed germination by enhancing the proteasome-mediated destruction of RGL2 (for RGA-LIKE2), a key DELLA factor repressing germination. By contrast, ABA blocks germination by inducing ABI5 (for ABA-INSENSITIVE5), a basic domain/leucine zipper transcription factor repressing germination.

Silencing of the major family of NBS-LRR-encoding genes in lettuce results in the loss of multiple resistance specificities.

The RGC2 gene cluster in lettuce (Lactuca sativa) is one of the largest known families of genes encoding nucleotide binding site-leucine-rich repeat (NBS-LRR) proteins. One of its members, RGC2B, encodes Dm3 which determines resistance to downy mildew caused by the oomycete Bremia lactucae carrying the cognate avirulence gene, Avr3. We developed an efficient strategy for analysis of this large family of low expressed genes using post-transcriptional gene silencing (PTGS).