Biology subjects

Valentine, T. A.

Publications and source records attributed to Valentine, T. A..

5 recordsLinked to original sources

bioRxiv2026

Cytokinin regulates the gravitropic setpoint angle of seminal roots in barley and wheat

Plant root growth angle determines the spatial distribution of roots in soil and thereby influences access to water and nutrients when these resources are heterogeneously distributed. In barley, multiple seminal roots emerge at distinct gravitropic setpoint angles (GSAs) and they reliably re-establish their characteristic growth angles following reorientation, indicating robust intrinsic control. However, the molecular basis underlying GSA variation among roots within a single root system remains unknown. Here, we combined individual root type-specific transcriptomics with laser-capture microdissection to profile gravity-responsive zones (root cap, meristem, and elongation zone). We identified two CYTOKININ OXIDASE/DEHYDROGENASE (CKX) genes whose expression in the root cap was associated with root-specific GSA. Functional analysis showed that ckx mutants, which show higher cytokinin levels, exhibit significantly steeper seminal root GSAs, implicating cytokinin catabolism in root angle regulation. Consistent with this, exogenous cytokinin treatment induced a dose-dependent steepening in root angle in barley. Analyses of gravitropic curvature after gravistimulation further showed that ckx mutants exhibit altered gravitropic responses, indicating that CKX-mediated regulation of the root angle depends on gravity-responsive pathways. Notably, GSA-associated CKX expression patterns and cytokinin-dependent root angle responses were also observed in wheat, suggesting a conservation of this mechanism across cereals. Together, these findings identify cytokinin as a key regulator of root specific setpoint angles within a root system architecture, with potential implications for optimizing crop resource acquisition and yield.

plant biology↗

bioRxiv2020

Stressful times in a climate crisis: how will aphids respond to more frequent drought?

AimAphids are abundant in natural and managed vegetation, supporting a diverse community of organisms and causing damage to agricultural crops. Using a meta-analysis approach, we aimed to advance understanding of how increased drought incidence will affect this ecologically and economically important insect group, and to characterise the underlying mechanisms. LocationGlobal. Time period1958-2020. Major taxa studiedAphids. MethodsWe used qualitative and quantitative synthesis techniques to determine whether drought stress has a negative, positive, or null effect on aphid fitness. We examined these effects in relation to 1) aphid biology, 2) the aphid-plant. species combination. We compiled two datasets: 1) a "global" dataset (n = 55 from 55 published studies) comprising one pooled effect size per study, and 2) an "expanded" dataset (n = 93) containing multiple datapoints per study, separated into different measures of aphid fitness but pooled across aphid-plant combinations. Where reported, we extracted data on the effect of drought on plant vigour, and plant tissue concentrations of nutrients and defensive compounds, to capture the potential causes of aphid responses. ResultsAcross all studies ("global" dataset), drought stress had a negative effect on aphid fitness: Hedges g = -0.57; 95% confidence interval (CI95) = {+/-}0.31. The "expanded" dataset indicated that, on average, drought stress reduced aphid fecundity (g = - 0.98; CI95 = {+/-}0.50) and increased development time (g = 1.13; CI95 = {+/-}1.02). Furthermore, drought stress had a negative impact on plant vigour (g = -7.06; CI95 = {+/-}2.86) and increased plant concentrations of defensive chemicals (g = 3.14; CI95 = {+/-}3.14). Main conclusionsAphid fitness is typically reduced under drought, associated with reduced plant vigour and increased chemical defence in drought-stressed plants. We propose a conceptual model to predict drought effects on aphid fitness in relation to plant vigour and defence.

ecology↗

bioRxiv2019

A fitness cost resulting from Hamiltonella defensa infection is associated with altered probing and feeding behaviour in Rhopalosiphum padi

Aphids frequently associate with facultative endosymbiotic bacteria which influence aphid physiology in myriad ways. Endosymbiont infection can increase aphid resistance against parasitoids and pathogens, modulate plant responses to aphid feeding, and promote aphid virulence. These endosymbiotic relationships can also decrease aphid fitness in the absence of natural enemies or when feeding on less suitable plant types. Here, we use the Electrical Penetration Graph (EPG) technique to monitor feeding behaviour of four genetically-similar clonal lines of a cereal-feeding aphid, Rhopalosiphum padi, differentially infected (+/-) with the facultative protective endosymbiont, Hamiltonella defensa, to understand how physiological processes at the aphid-plant interface are affected by endosymbiont infection. Endosymbiont-infected aphids exhibited altered probing and feeding patterns compared with uninfected aphids, characterised by a two-fold increase in the number of plant cell punctures, a 50% reduction in the duration of each cellular puncture, and a greater probability of achieving sustained ingestion of plant phloem. Feeding behaviour was altered further by host plant identity: endosymbiont-infected aphids spent less time probing into plant tissue, required twice as many probes into plant tissue to reach plant phloem, and showed a 44% reduction in phloem ingestion when feeding on the partially-resistant wild relative of barley, Hordeum spontaneum 5, compared with a commercial barley cultivar. These observations might explain reduced growth of H. defensa-infected aphids on the former host plant. This study is the first to demonstrate a physiological mechanism at the aphid-plant interface contributing to endosymbiont effects on aphid fitness on different quality plants through altered aphid feeding behaviour.\n\nSummaryReduced performance of aphids infected with a common facultative endosymbiont on poor quality plants may be explained by changes in aphid probing behaviour and decreased phloem sap ingestion.

physiology↗

bioRxiv2019

Partial-resistance against aphids in wild barley reduces the oviposition success of the generalist parasitoid, Aphidius colemani

Aphids are significant agricultural pests of cereal crops with a worldwide distribution. The control of aphids in agricultural systems is currently heavily reliant on insecticidal compounds, but it is becoming increasingly apparent that chemical-based control of agricultural pests has far-reaching unintended consequences on agro-ecosystems. As a result, more sustainable means of aphid control are becoming increasingly desirable. Potential options include increasing plant resistance against aphids, promoting biocontrol, and the combined use of both strategies. When used together it is important to understand how, and to what extent, increased plant resistance against aphids affects the success of biocontrol agents. In this current study, we examine how partial-resistance against cereal aphids in a wild relative of barley, Hordeum spontaneum 5 (Hsp5), affects the success of the common parasitoid of cereal aphids, Aphidius colemani. We show that the parasitism success of A. colemani attacking nymphs of the bird cherry-oat aphid, Rhopalosiphum padi, contained on Hsp5 is reduced compared with the parasitism success of wasps attacking R. padi nymphs feeding on a susceptible modern cultivar of barley, H. vulgare cv. Concerto. Explanta parasitism assays showed that the in parasitoid success is a direct effect of the plant environment (such as differential architectural traits), rather than an indirect effect dur to a decrease in aphid suitability resulting from increased resistance against aphids in Hsp5. Our study highlights the importance of understanding the direct and indirect effects of plant resistance against aphids on biocontrol strategies.

plant biology↗

bioRxiv2018

Partial-resistance against aphids in wild barley involves phloem and mesophyll-based defences

Aphids, including the bird cherry-oat aphid (Rhopalosiphum padi), are significant agricultural pests. Aphid populations are typically controlled using insecticides, but there is increasing demand for more sustainable pest management practices. The wild relative of barley, Hordeum spontaneum 5 (Hsp5) has been described as partially-resistant to R. padi. Partial-resistance is proposed to involve higher thionin and lipoxygenase gene expression. However, the underlying mechanistic processes are unknown. In this study we compared Hsp5 with a susceptible cultivar of barley (Concerto) to test the extent to which partial-resistance affects aphid fitness. We used the electrical penetration graph technique to monitor R. padi feeding patterns to elucidate the tissue location of partial-resistance factors alongside molecular and biochemical analyses to identify potential mechanisms. We show that partial-resistance in Hsp5 extends to three aphid species and is mediated by phloem/mesophyll-based factors, leading to a three-fold increase in the time aphids take to establish sustained phloem ingestion. Partial-resistance likely involves elevated expression of defence and phytohormone genes alongside altered phloem amino acid composition. Further work is required to establish the function of these traits, however this study highlights plant tissues which are important in conferring broad-spectrum partial-resistance against aphids in barley.\n\nHighlightPartial-resistance against aphids in wild barley is based in the mesophyll and vascular tissue and is potentially associated with higher basal defence gene expression and altered phloem amino acid composition.

plant biology↗