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/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

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

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

Flowering roots: Insensitive Root Growth 1 contributes to photoperiod-induced root responses in Arabidopsis.

The capacity to perceive and respond to seasonal changes of day length is essential for flowering plants. Under favourable photoperiod, a mobile stimulus synthesized in leaves moves to the shoot apex and triggers the expression of genes required for the transition to flower initiation. Although transition from vegetative to reproductive state also encompasses a transcriptional response in roots, the internal signalling pathways and how root system architecture adjusts to this changing status remain elusive. Here we show in Arabidopsis that root growth rate increases upon a transfer to flowering-inductive long days while remaining constant under short days. To elucidate genetic components of this response, we performed a meta-analysis of available root-growth and flowering-related arrays and selected genes with overlapping transcriptional profiles for further analyses. Loss of function in a member of the basic leucine zipper transcription factor gene family, hereafter named Insensitive Root Growth-1 (IRG1), was found to suppress photoperiod-response of root growth with no defect in flowering time. We show that sucrose, but neither glucose nor mannitol in the growth medium under long days, is needed to trigger this response. In addition, extending the photoperiod with non-photosynthetic far red light had no effect on root growth of irg-1 mutant, alike wild type Col-0. The expression level of IRG1 in the roots remains low during the daytime and peaks late at night, suggesting that this gene is regulated by the clock’s evening loop. Taken together, our results suggest that IRG1 may be involved in sucrose-mediated stimulation of root growth during the night phase in Arabidopsis. The functional characterisation of IRG1 is currently underway

Overexpression of the tomato JOINTLESS gene alters flowering

Abscission is an important mechanism that allows plants to separate unfertilized flowers, ripe fruits or damage organs from the plant. In tomato, jointless (j) and jointless-2 (j-2) mutations leads a lack of abscission zone (AZ) in the flower pedicel, which will avoid falling of ripe fruits and prevent loss of yield. Both J and J-2 are genes encoding MADS-box transcription factors (Mao et al. 2000; Gomez-Roldan et al., 2017) that can interact with other MADS-box proteins, like MACROCALYX (MC), forming a multimeric complex able to regulate the AZ formation (Liu et al. 2014). In addition to the AZ formation, J also plays a role in flowering architecture and meristem fate. This last role is consistent with the functions of the closets homologs of J in Arabidopsis, SHORT VEGETATIVE PHASE (SVP) and AGAMOUS LIKE 24 (AGL24) (Gregis et al. 2006). Mutation of J leads to a faster flower maturation and a reversion to the vegetative state of the inflorescence meristems, which originates leafy inflorescences (Périlleux et al. 2014). Nevertheless, J is not the only one that regulates at the same time AZ formation and meristem functions. Other transcription factors such as the tomato homolog of WUSHEL (LeWUS), GOBLET (GOB), LATERAL SUPPRESSOR (Ls) and Blind (Bl) are involved in those pathways (Nakano et al. 2012; Nakano et al. 2013). We have generated transgenic plants that overexpress J (35S:J) showing changes in the inflorescence architecture and AZ development, but also having interesting phenotypes in axillary development and leaf complexity. These results suggest that J takes part in different pathways and regulate several downstream genes. Our goal is to identify and study the targets of the J transcription factor in order to understand its functions in the tomato plant

Analysing the molecular and phenotypic effects of overexpression of JOINTLESS gene in tomato

JOINTLESS (J) is a MADS-box gene that regulates inflorescence traits in tomato: its mutation reduces the number of flowers in the inflorescence, which reverts to leaf initiation, and suppresses the abscission zone (AZ) in the flower pedicels. It has been shown that the J protein physically interacts with other MADS-box transcription factors, MACROCALYX (MC) and JOINTLESS-2 (J-2) previously known as SlMBP21. Their putative targets are genes involved in AZ initiation since j, j-2 and mc mutants share this common phenotype. For a better understanding of the role of J in the architecture of the inflorescence, overexpression lines have been generated. A RNA-seq approach, comparing overexpression and wild-type lines, has been used to identify potential J-targets and better understand its molecular function