Roots Withstanding their Environment: Exploiting Root System Architecture Responses to Abiotic Stress to Improve Crop Tolerance

To face future challenges in crop production dictated by global climate changes, breeders and plant researchers collaborate to develop productive crops that are able to withstand a wide range of biotic and abiotic stresses. However, crop selection is often focused on shoot performance alone, as observation of root properties is more complex and asks for artificial and extensive phenotyping platforms. In addition, most root research focuses on development, while a direct link to the functionality of plasticity in root development for tolerance is often lacking. In this paper we review the currently known root system architecture (RSA) responses in Arabidopsis and a number of crop species to a range of abiotic stresses, including nutrient limitation, drought, salinity, flooding, and extreme temperatures. For each of these stresses, the key molecular and cellular mechanisms underlying the RSA response are highlighted. To explore the relevance for crop selection, we especially review and discuss studies linking root architectural responses to stress tolerance. This will provide a first step toward understanding the relevance of adaptive root development for a plant's response to its environment. We suggest that functional evidence on the role of root plasticity will support breeders in their efforts to include root properties in their current selection pipeline for abiotic stress tolerance, aimed to improve the robustness of crops

Out of Shape During Stress: A Key Role for Auxin

In most abiotic stress conditions, including salinity and water deficit, the developmental plasticity of the plant root is regulated by the phytohormone auxin. Changes in auxin concentration are often attributed to changes in shoot-derived long-distance auxin flow. However, recent evidence suggests important contributions by short-distance auxin transport from local storage and local auxin biosynthesis, conjugation, and oxidation during abiotic stress. We discuss here current knowledge on long-distance auxin transport in stress responses, and subsequently debate how short-distance auxin transport and indole-3-acetic acid (IAA) metabolism play a role in influencing eventual auxin accumulation and signaling patterns. Our analysis stresses the importance of considering all these components together and highlights the use of mathematical modeling for predictions of plant physiological responses

The societal roles and responsibilities of plant scientists in the context of genome-edited crops

Societal Impact Statement The societal debate on the use of genome-edited crops has been polarised from the start. While policymakers struggle to democratically resolve this dilemma, plant scientists have been criticised for taking up advocative roles and thereby risking further polarisation. This study demonstrates how plant scientists themselves perceive their roles and responsibilities. Indeed, those scientists active in the debate were found to fulfil advocative roles, and there seems to be an underlying, persistent?and very traditional?view on roles and responsibilities of scientists within the community. Critical reflection on this view is required for better democratic dialogue and decision-making. More interdisciplinary interaction could facilitate this reflection. Summary In this paper, we examine how plant scientists from Wageningen University and Research (WUR) demarcate their roles and responsibilities in relation to the societal impact of their research, in response to calls for public legitimacy of their research, and within the societal debate on the governance of genome-edited crops (GE crops) in Europe. We analysed 16 semi-structured interviews, 5-day journals, and (social) media contributions of plant scientists at WUR. Our study demonstrates that the perceived roles and responsibilities of the interviewees were aligned with the ideal of the scientist as value-free, as separate from society, and as producing knowledge that leads to unproblematic societal benefits through industry. When confronted with the polarised debate on the governance of genome editing (GE) technology, the reflexivity that our respondents had demonstrated in general, tended to be dispersed. Respondents rarely considered the GE crop debate, or their own position, to be value-based. Those respondents active in the debate were found to fulfil advocative roles, and they struggled to recognise the validity of viewpoints other than their own. We hypothesise that this decreased reflexive capacity is a product of the long-term polarisation of the GM/GE debate, mediated by both their conceptual alignment with the linear model of innovation and their limited interactions outside of their field. In order to better align the perspectives of social and natural scientists on the topic of science-responsibility, and to constructively contribute to the debate on GE crops, we argue for more interaction between the these two communities

Chemical genetics approach identifies abnormal inflorescence meristem 1 as a putative target of a novel sulfonamide that protects catalase2-deficient Arabidopsis against photorespiratory stress

Alterations of hydrogen peroxide (H2O2) levels have a profound impact on numerous signaling cascades orchestrating plant growth, development, and stress signaling, including programmed cell death. To expand the repertoire of known molecular mechanisms implicated in H2O2 signaling, we performed a forward chemical screen to identify small molecules that could alleviate the photorespiratory-induced cell death phenotype of Arabidopsisthaliana mutants lacking H2O2-scavenging capacity by peroxisomal catalase2. Here, we report the characterization of pakerine, an m-sulfamoyl benzamide from the sulfonamide family. Pakerine alleviates the cell death phenotype of cat2 mutants exposed to photorespiration-promoting conditions and delays dark-induced senescence in wild-type Arabidopsis leaves. By using a combination of transcriptomics, metabolomics, and affinity purification, we identified abnormal inflorescence meristem 1 (AIM1) as a putative protein target of pakerine. AIM1 is a 3-hydroxyacyl-CoA dehydrogenase involved in fatty acid β-oxidation that contributes to jasmonic acid (JA) and salicylic acid (SA) biosynthesis. Whereas intact JA biosynthesis was not required for pakerine bioactivity, our results point toward a role for β-oxidation-dependent SA production in the execution of H2O2-mediated cell death

Phosphate-dependent root system architecture responses to salt stress

Nutrient availability and salinity of the soil affect growth and development of plant roots. Here, we describe how phosphate availability affects root system architecture (RSA) of Arabidopsis and how phosphate levels modulate responses of the root to salt stress. Phosphate (Pi) starvation reduced main root length and increased the number of lateral roots of Arabidopsis Col-0 seedlings. In combination with salt, low Pi dampened the inhibiting effect of mild salt stress (75mM) on all measured RSA components. At higher NaCl concentrations, the Pi deprivation response prevailed over the salt stress only for lateral root elongation. The Pi deprivation response of lateral roots appeared to be oppositely affected by abscisic acid (ABA) signaling compared to the salt stress response. Natural variation in the response to the combination treatment of salt and Pi starvation within 330 Arabidopsis accessions could be grouped into four response patterns. When exposed to double stress, in general lateral roots prioritized responses to salt, while the effect on main root traits was additive. Interestingly, these patterns were not identical for all accessions studied and multiple strategies to integrate the signals from Pi deprivation and salinity were identified. By Genome Wide Association Mapping (GWAS) 13 genomic loci were identified as putative factors integrating responses to salt stress and Pi starvation. From our experiments, we conclude that Pi starvation interferes with salt responses mainly at the level of lateral roots and that large natural variation exists in the available genetic repertoire of accessions to handle the combination of stresses

Soil salinity inhibits plant shade avoidance

Global food production is set to keep increasing despite a predicted decrease in total arable land. To achieve higher production, denser planting will be required on increasingly degraded soils. When grown in dense stands, crops elongate and raise their leaves in an effort to reach sunlight, a process termed shade-avoidance. Shade is perceived by a reduction in the ratio of red (R) to (FR) light and results in the stabilisation of a class of transcription factors known as PHYTOCHROME INTERACTING FACTORs (PIFs). PIFs activate the expression of auxin biosynthesis genes and enhance auxin sensitivity, which promotes cell wall loosening and drives elongation growth. Despite our molecular understanding of shade-induced growth, little is known about how this developmental programme is integrated with other environmental factors. Here we demonstrate that low levels of NaCl in soil strongly impair the ability of plants to respond to shade. This block is dependent upon abscisic acid (ABA) signalling and the canonical ABA signalling pathway. Low R:FR light enhances the expression of a positive regulator of the brassinosteroid (BR) signalling pathway, BRASSINOSTEROID SIGNALLING KINASE 5 (BSK5). We found that ABA inhibits BSK5 up-regulation and interferes with GSK3-like kinase inactivation by the BR pathway, thus leading to a suppression of PIF function. By demonstrating a link between the ABA and BR-signalling pathways this study provides an important step forward in our understanding of how environmental cues are integrated into plant development