Multi-seasonal effects of warming and elevated CO₂ on the physiology, growth and production of mature, field grown, Shiraz grapevines

Abstract: Industry concerns in Australia about the impacts of climate change have, to date, focused on the effects of warming, particularly shorter maturation periods. The effects of elevated CO2 concentration (eCO2) on C3 plant physiology have been extensively studied and suggest that eCO2 impacts on viticulture could affect grapevine shoot growth, fruit production and fruit composition. We previously used open top chambers (OTC) with an active heating system to study the effects of elevated air temperature (eTemp) on mature grapevines in the field. This system was augmented with the ability to elevate atmospheric CO2 and established in a mature Shiraz vineyard in a factorial combination of eTemp and eCO2. Three seasons of observations on the eTemp only treatment corroborated our previous study; all aspects of phenology were advanced, but leaf function was largely unaffected. In contrast, the effects of eCO2 on phenology were small in the first season, but increased over the subsequent two seasons. Interactive effects of the treatments on gas exchange were observed; photosynthesis rates were significantly higher in the eCO2+eTemp treatment, compared to eCO2 alone, suggesting that the likely future climate will have a larger impact on viticulture than might be predicted from experiments examining only one of these factors

Canopy temperature of high‐nitrogen water‐stressed cotton

Australian cotton (Gossypium hirsutum L.) farmers are adopting canopy temperature (Tc)-based irrigation scheduling as a decision support tool to improve on-farm production. High N supply, characteristic of the high-yielding, furrow-irrigated cotton system of Australia, might alter cotton Tc with implications for irrigation. We examined growth, physiological, and biochemical traits and changes in Tc of well-watered and water-stressed cotton plants supplied with high to excessive levels of N under glasshouse conditions. We also examined Tc, lint yield, and fiber quality of furrow-irrigated cotton crop supplied with high N. In the glasshouse and under well-watered conditions, high N supply stimulated plant growth and increased stomatal conductance and photosynthesis, resulting in cooler Tc. Under water deficit stress, high N also stimulated growth, increasing plant water demand and thus vulnerability to water stress, which manifested as warmer Tc. Water-stressed plants supplied high N also showed reduced stomatal conductance, lower leaf water potential, and greater accumulation of leaf and xylem sap abscisic acid. Furrow-irrigated crops supplied higher N also had higher Tc, but there was no gain in lint yield and fiber quality. The influence of high N on cotton Tc suggests that the need for accurate and reliable Tc-based irrigation scheduling is paramount

Barley Plants Overexpressing Ferrochelatases (HvFC1 and HvFC2) Show Improved Photosynthetic Rates and Have Reduced Photo-Oxidative Damage under Drought Stress than Non-Transgenic Controls

We investigated the roles of two Ferrochelatases (FCs), which encode the terminal enzyme for heme biosynthesis, in drought and oxidative stress tolerance in model cereal plant barley (Hordeum vulgare). Three independent transgenic lines ectopically overexpressing either barley FC1 or FC2 were selected and evaluated under well-watered, drought, and oxidative stress conditions. Both HvFC1 and HvFC2 overexpressing transgenics showed delayed wilting and maintained higher photosynthetic performance relative to controls, after exposure to soil dehydration. In each case, HvFC overexpression significantly upregulated the nuclear genes associated with detoxification of reactive oxygen species (ROS) upon drought stress. Overexpression of HvFCs, also suppressed photo-oxidative damage induced by the deregulated tetrapyrrole biosynthesis mutant tigrinad12. Previous studies suggest that only FC1 is implicated in stress defense responses, however, our study demonstrated that both FC1 and FC2 affect drought stress tolerance. As FC-derived free heme was proposed as a chloroplast-to-nuclear signal, heme could act as an important signal, stimulating drought responsive nuclear gene expression. This study also highlighted tetrapyrrole biosynthetic enzymes as potential targets for engineering improved crop performance, both in well-watered and water-limited environments

Altering Tetrapyrrole Biosynthesis by Overexpressing Ferrochelatases (Fc1 and Fc2) Improves Photosynthetic Efficiency in Transgenic Barley

Ferrochelatase (FC) is the terminal enzyme of heme biosynthesis. In photosynthetic organisms studied so far, there is evidence for two FC isoforms, which are encoded by two genes (FC1 and FC2). Previous studies suggest that these two genes are required for the production of two physiologically distinct heme pools with only FC2-derived heme involved in photosynthesis. We characterised two FCs in barley (Hordeum vulgare L.). The two HvFC isoforms share a common catalytic domain, but HvFC2 additionally contains a C-terminal chlorophyll a/b binding (CAB) domain. Both HvFCs are highly expressed in photosynthetic tissues, with HvFC1 transcripts also being abundant in non-photosynthetic tissues. To determine whether these isoforms differentially affect photosynthesis, transgenic barley ectopically overexpressing HvFC1 and HvFC2 were generated and evaluated for photosynthetic performance. In each case, transgenics exhibited improved photosynthetic rate (Asat), stomatal conductance (gs) and carboxylation efficiency (CE), showing that both FC1 and FC2 play important roles in photosynthesis. Our finding that modified FC expression can improve photosynthesis up to ~13% under controlled growth conditions now requires further research to determine if this can be translated to improved yield performance under field conditions

Insights into Long-Term Acclimation Strategies of Grapevines (<i>Vitis vinifera</i> L.) in Response to Multi-Decadal Cyclical Drought

Changing climatic conditions across Australia’s viticulture regions is placing increasing pressure on resources such as water and energy for irrigation. Therefore, there is a pressing need to identify superior drought tolerant grapevine clones by exploring the extensive genetic diversity of early European clones in old vineyards. Previously, in a field trial, we identified drought-tolerant (DT) dry-farmed Cabernet Sauvignon clones that had higher intrinsic water use efficiency (WUEi) under prolonged soil moisture deficiency compared to drought-sensitive (DS) clones. To investigate whether the field-grown clones have been primed and confer the drought-tolerant phenotypes to their subsequent vegetative progenies, we evaluated the drought responses of DT and DS progenies under two sequential drought events in a glasshouse alongside progenies of commercial clones. The DT clonal progenies exhibited improved gas exchange, photosynthetic performance and WUEi under recurrent drought events relative to DS clonal progenies. Concentration of a natural priming agent, γ-amino butyric acid (GABA), was significantly higher in DT progenies relative to other progenies under drought. Although DT and commercial clones displayed similar drought acclimation responses, their underlying hydraulic, stomatal and photosynthetic regulatory mechanisms were quite distinct. Our study provides fundamental insights into potential intergenerational priming mechanisms in grapevine

Fast Phenomics in Vineyards: Development of GRover, the Grapevine Rover, and LiDAR for Assessing Grapevine Traits in the Field

This paper introduces GRover (the grapevine rover), an adaptable mobile platform for the deployment and testing of proximal imaging sensors in vineyards for the non-destructive assessment of trunk and cordon volume and pruning weight. A SICK LMS-400 light detection and ranging (LiDAR) radar mounted on GRover was capable of producing precise (±3 mm) 3D point clouds of vine rows. Vineyard scans of the grapevine variety Shiraz grown under different management systems at two separate locations have demonstrated that GRover is able to successfully reproduce a variety of vine structures. Correlations of pruning weight and vine wood (trunk and cordon) volume with LiDAR scans have resulted in high coefficients of determination (R2 = 0.91 for pruning weight; 0.76 for wood volume). This is the first time that a LiDAR of this type has been extensively tested in vineyards. Its high scanning rate, eye safe laser and ability to distinguish tissue types make it an appealing option for further development to offer breeders, and potentially growers, quantified measurements of traits that otherwise would be difficult to determine.This project was partly funded by Australia’s grape growers and winemakers through their investment body Wine Australia with matching funds from the Australian Federal Government. Additional funds for this work were provided by Commonwealth Scientific and Industrial Research Organisation (CSIRO).Peer reviewe

Gene body demethylation increases expression and is associated with self-pruning during grape genome duplication

A colchicine-induced autotetraploid grapevine exhibiting potentially valuable agronomic traits for grape production and breeding, including self-pruning, was identified. This study investigated DNA methylation variation and its role in gene expression during self-pruning in the autotetraploid grapevine. We used RNA-Seq to estimate differentially expressed genes between diploid and autotetraploid grapevine shoot tips. The genes showing increases in the autotetraploid were mainly related to stress response pathways, whereas those showing decreases in the autotetraploid were related to biological metabolism and biosynthesis. Whole-genome bisulfite sequencing was performed to produce single-base methylomes for the diploid and autotetraploid grapevines. Comparison between the methylomes revealed that they were conserved in CG and CHG contexts. In the autotetraploid grapevine, hypodifferentially methylated regions (DMRs) and hyper-DMRs in the gene body increased or decreased gene expression, respectively. Our results indicated that a hypo-DMR in the ACO1 gene body increased its expression and might promote self-pruning. This study reports that hypo-DMRs in the gene body increase gene expression in plants and reveals the mechanism underlying the changes in the modifications affecting gene expression during genome duplication. Overall, our results provide valuable information for understanding the relationships between DNA methylation, gene expression, and autotetraploid breeding in grape