Barley <i>lys3</i> mutants are unique amongst shrunken-endosperm mutants in having abnormally large embryos

Many shrunken endosperm mutants of barley (Hordeum vulgare L.) have been described and several of these are known to have lesions in starch biosynthesis genes. Here we confirm that one type of shrunken endosperm mutant, lys3 (so called because it was first identified as a high-lysine mutant) has an additional phenotype: as well as shrunken endosperm it also has enlarged embryos. The lys3 embryos have a dry weight that is 50?150% larger than normal. Observations of developing lys3 embryos suggest that they undergo a form of premature germination and the mature lys3 grains show reduced dormancy. In many respects, the phenotype of barley lys3 is similar to that of rice GIANT EMBRYO mutants (affected in the OsGE gene). However, the barley orthologue of OsGE is located on a different chromosome from Lys3. Together these results suggest that the gene underlying Lys3 is unlikely to encode a starch biosynthesis protein but rather a protein influencing grain developmentpublishersversionPeer reviewe

The xerobranching response represses lateral root formation when roots are not in contact with water

Efficient soil exploration by roots represents an important target for crop improvement and food security [1, 2]. Lateral root (LR) formation is a key trait for optimising soil foraging for crucial resources such as water and nutrients. Here, we report an adaptive response termed xerobranching, exhibited by cereal roots, that represses branching when root tips are not in contact with wet soil. Non-invasive X-ray microCT imaging revealed that cereal roots rapidly repress LR formation as they enter an air space within a soil profile and are no longer in contact with water. Transcript profiling of cereal root tips revealed that transient water deficit triggers the abscisic acid (ABA) response pathway. In agreement with this, exogenous ABA treatment can mimic repression of LR formation under transient water deficit. Genetic analysis in Arabidopsis revealed that ABA repression of LR formation requires the PYR/PYL/RCARdependent signalling pathway. Our findings suggest that ABA acts as the key signal regulating xerobranching. We conclude that this new ABA-dependent adaptive mechanism allows roots to rapidly respond to changes in water availability in their local micro-environment and to use internal resources efficiently

The xerobranching response represses lateral root formation when roots are not in contact with water

Efficient soil exploration by roots represents an important target for crop improvement and food security [1, 2]. Lateral root (LR) formation is a key trait for optimising soil foraging for crucial resources such as water and nutrients. Here, we report an adaptive response termed xerobranching, exhibited by cereal roots, that represses branching when root tips are not in contact with wet soil. Non-invasive X-ray microCT imaging revealed that cereal roots rapidly repress LR formation as they enter an air space within a soil profile and are no longer in contact with water. Transcript profiling of cereal root tips revealed that transient water deficit triggers the abscisic acid (ABA) response pathway. In agreement with this, exogenous ABA treatment can mimic repression of LR formation under transient water deficit. Genetic analysis in Arabidopsis revealed that ABA repression of LR formation requires the PYR/PYL/RCAR-dependent signalling pathway. Our findings suggest that ABA acts as the key signal regulating xerobranching. We conclude that this new ABA-dependent adaptive mechanism allows roots to rapidly respond to changes in water availability in their local micro-environment and to use internal resources efficiently

Branching out in roots: uncovering form, function, and regulation

Root branching is critical for plants to secure anchorage and ensure the supply of water, minerals, and nutrients. To date, research on root branching has focused on lateral root development in young seedlings. However, many other programs of postembryonic root organogenesis exist in angiosperms. In cereal crops, the majority of the mature root system is composed of several classes of adventitious roots that include crown roots and brace roots. In this Update, we initially describe the diversity of postembryonic root forms. Next, we review recent advances in our understanding of the genes, signals, and mechanisms regulating lateral root and adventitious root branching in the plant models Arabidopsis (Arabidopsis thaliana), maize (Zea mays), and rice (Oryza sativa). While many common signals, regulatory components, and mechanisms have been identified that control the initiation, morphogenesis, and emergence of new lateral and adventitious root organs, much more remains to be done. We conclude by discussing the challenges and opportunities facing root branching research

Comparative study of molecular mechanisms underlying Arabidopsis and cereals root architecture

Plant roots are required to anchor the plant in the soil, acquire water and nutrients and respond to biotic and abiotic stimuli. Root branching contributes largely to the morphological plasticy of the root system. Auxin is an important plant hormone involved in lateral root (LR) development and root gravitropism. In this thesis, an in silico translational approach was employed to identify selected auxin-related genes in barely. We focused our work on auxin transporters that are involved in plant response to environmental stimuli. AUX1 and LAX3 were identified in barley and subsequently characterised. These experiments revealed the maintenance of AUX/LAX developmental function between highly divergent plant species. Reactive oxygen species (ROS) were recently proposed to contribute to auxin-mediated LR formation, however the nature of their involvement remains elusive. We show that H2O2 accumulates in middle lamellae of cells overlying LR primordia and progressively creates a fine layer around the emerging LR primordia. Our results lead us to propose that ROS contribute to LR emergence by influencing cell wall plasticity. We finally show that the Respiratory burst oxidase homologs (Rboh) gene family are likely contributors to a fine-tuned extracellular ROS balance during LR emergence. Abscisic acid (ABA) is another plant hormone known to modulate LR development and to regulate responses to environmental stimuli. We demonstrated that ABA response pathways act downstream of water deficit in the acropetal root zone and that ABA is likely to mediate LR repression. Those results lead to a model of root branching adaptation to local soil porosity.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201

Architectural and developmental changes due to overexpression of the JOINTLESS gene in tomato

Inflorescence architecture shows huge variation among flowering plants, especially in the amount of flowers and branching degree. In tomato, the formation of the inflorescence follows a sympodial pattern : the shoot apical meristem (SAM) acquires a floral meristem (FM) fate and forms the first flower while a lateral inflorescence meristem (IM) is initiated, which itself matures into a FM when a second IM is initiated, and so on. This sympodial mode of inflorescence development is regulated by a complex genetic network, which remains to be elucidated. Tomato is also used as a model in the study of abscission, an important process by which plants can isolate and drop different parts such as non fertilized flowers, damaged organs or ripe fruits. The lack of fruit abscission zone – the “jointless” phenotype – is associated with the j and j-2 mutations, which impair the function of two MADS-box genes: JOINTLESS (J) and SlMBP21. We are interested in understanding the functions of J, because j knock-out mutation does not only alter the abscission zone but causes inflorescence reversion to leaf production after the initiation of few flowers. Our goal is therefore to identify the targets of J by different molecular approaches.Study of jointless gene in the inflorecence architecture of tomat