Integrative Plant Physiology for Climate-Resilient Crops

Barbara Demmig-Adams and William W. Adams III

Abstract

The need to develop climate-resilient crops is intensifying as extreme weather events become more common. To ensure future global food security, crops need to be developed that maintain high productivity under challenging conditions with respect to, e.g., temperature and precipitation levels. To accomplish these goals, collaboration across disciplines, approaches, and scales needs to be escalated. Promising targets of such integrative approaches include (1) characterization of specific traits in the context of the whole plant and its source-sink interactions via major feedback loops and signaling networks; (2) identification of possible trade-offs via characterization of putative adaptive traits in the context of ecology and evolution, i.e., under more than one environmental condition and including comparison of genotypes adapted to a range of environmental conditions; and (3) development of high-throughput phenotypic characterization than can be coupled with genomics approaches. In addition to providing an overview of current challenges to plant biology and promising avenues to address these, examples drawn from the work of our group will be presented. Links between photosynthetic productivity in extreme environments, redox-regulatory signaling networks, and the vascular network for water import into and sugar-export from leaves will be examined. Specifically, antioxidant mutants with decreased levels of either thermal energy dissipation in the chloroplast or decreased foliar tocopherol levels will be used to illustrate how an altered redox balance affects photosynthesis, transpiration, anatomical/ultrastructural features of foliar water- and sugar-transport infrastructure, and growth.

Keywords: Photosynthetic productivity; source-sink balance; redox signaling; antioxidant mutants


The ups and downs of root-shoot communication in planta

Ian C. Dodd A, Jaime Puertolas A, Pedro Castro A, Alfonso Albacete B, Francisco Perez-Alfocea B

E-mail: I.Dodd@lancaster.ac.uk

A Lancaster Environment Centre, Lancaster LA1 4YQ, United Kingdom

B CEBAS-CSIC Murcia, Spain

As sessile organisms, plants need to adapt to both above-ground and below-ground environmental stresses to optimise their physiological performance and fitness. Such adaptation relies on communication between the roots and the shoots, which exploits multiple long-distance signals (water relations, ions, peptides, RNAs and phytohormones). Various techniques have been developed to sample transport fluids (xylem and phloem saps) to measure such signalling 1, with the advent of sensitive multi-analyte phytohormone analysis 2 proving especially powerful to elucidate plant stress responses. Often, changes in xylem sap composition are interpreted as evidence of altered root-to-shoot signalling even though many phytohormones are synthesised in both root and shoot tissues. Reciprocal grafting of mutants/transgenics (with compromised or enhanced phytohormone synthesis) and their respective wild-types can provide less equivocal evidence of bona fide long distance signalling when root and shoot performance differs between chimeric and self-grafted plants 3. Furthermore, the surgical technique of girdling (removal of stem phloem tissue at the root-shoot junction) can suppress shoot-to-root signalling to evaluate its impact on root and shoot performance. Examples of experiments utilising either grafting or girdling will be presented to evaluate the importance of long-distance signalling in regulating plant responses to different abiotic stresses. Furthermore, examples where “signalling science” has been exploited in crop management will be considered.

References:

1 Dodd (2005) Plant & Soil 274, 257-275

2 Ghanem et al. (2008) J. Exp. Bot. 59, 3039-3050

3 Albacete et al. (2015) J. Exp. Bot. 66, 2211-2226

Keywords: girdling, grafting, phytohormones, stress


Elucidating and re-designing regulatory networks underlying plant-pathogen interaction

Elspeth Ransom, Gill Higgins, Fabian Vaistij, Ryan Carter and Katherine Denby

Department of Biology, University of York

Abstract

Plant responses to biotic stress involve large-scale transcriptional reprogramming. We are elucidating the gene regulatory networks underlying these transcriptional responses to pathogen infection using a combination of experimental and computational/mathematical tools. We generated high-resolution time series expression data from Arabidopsis leaves following infection with bacterial and fungal pathogens. These time series data sets have enabled us to identify transient changes in gene expression and resolve the chronology of plant defence responses. We have generated transcriptional network models predicting regulatory relationships between differentially expressed transcription factors and identified key regulators of the Arabidopsis defence response from our networks. Crucially many of these key regulators were not previously known to affect susceptibility to plant pathogens. Using simulations of the network models we are predicting how to re-wire the defence transcriptional network to increase the disease resistance of Arabidopsis, both by enhancing expression of positive regulators of defence as well as by strategies to prevent pathogen suppression of defence.

We have applied this time series-based network analysis gene discovery strategy to lettuce to predict genes conferring disease resistance against two fungal pathogens, Botrytis cinerea and Sclerotinia sclerotiorum, and speed up the breeding of these traits. Dual RNAseq time series enabled us to capture temporal transcriptome changes in both host and pathogen to investigate the how the lettuce defence response against these two pathogens is regulated, probe the molecular basis of plant-pathogen interaction and predict key regulators of virulence in the pathogens.

Keywords: gene regulatory network, disease resistance, network modelling, transcriptom


Plant acclimation to environmental stress using chemical compounds

Vasileios Fotopoulos, Chrystalla Antoniou, Andreas Savvides and Anastasis Christou

Abstract

Increased frequency of extreme environmental events resulting from global climatic changes remarkably influences plant growth and development. Close examination of plant-to-plant communication in nature has revealed the development of unique strategies from plants for responding to abiotic stress, with one of the most interesting being through priming for improved defense responses. The process of priming involves prior exposure to a biotic or abiotic stress factor making a plant more resistant to future exposure. Priming can also be achieved by applying natural or synthetic compounds which act as signaling transducers, ‘activating’ the plant’s defense system. An up-to-date overview will be presented describing the research carried out at the Cyprus University of Technology using priming agents towards induced acclimation of plants to environmental challenges. Focus will be given to NOSH-aspirin (NBS-1120), a patented nitric oxide- and hydrogen sulfide-releasing hybrid that additionally provides the pharmaceutical molecule acetylsalicylic acid. In addition, recent findings will be presented on the evaluation of chemical compounds that potentially display growth promoting properties in plants, closely related to our existing expertise and previous observations in priming against stress.

Keywords: plant priming; abiotic stress; antioxidants; reactive species


Breaking-dormancy and germination of seeds from the tropics: what are the microhabitat and temperature telling us?

Queila S. Garcia, Elisa M. Bicalho, Leilane C. Barreto

Seed germination is a complex and definitive step in plant life cycle largely influenced by environmental traits, such as light, temperature and water. In tropical areas, where temperature does not show major season variations, less is known about the processes of dormancy modulation and seed germination. Mainly due to the fact they are in this kind of regions, some species need a particular set of those traits, making local climate influences mandatory. This way, the markedly presence of microhabitats in tropical areas reveals uncommon responses on seed germination. This review approaches the particularities and crucial roles of environmental signaling on breaking-dormancy and seed germination of species from tropical areas. We discuss how microhabitats can influence on hormonal and biochemical control of seed breaking-dormancy and germination. Additionally, considering that dormancy cycles are an important mechanism for avoiding seed germination under unfavorable periods for seedling establishment and that they have been scarcely studied in tropical species, we also present how the interaction between soil temperature and humidity can modulate the acquisition and overcoming of secondary dormancy, interfering on dormancy cycles of important groups of species from Brazilian cerrado. These seeds acquire secondary dormancy during the rainy season (spring/summer, higher temperatures), when exposed to humidity, and lose it during the subsequent dry season (autumn/ winter, lower temperatures). Thus, the way these microhabitats, especially the variation of the humidity regime signals the acquisition and the overcoming of secondary dormancy, is well documented here.

Keywords: Brazilian cerrado, dormancy cycles, hormones, breaking-dormancy, soil humidity and temperature, tropical environments


Rice grain filling problems and its physiological and genetic regulations

Jianhua Zhang

Department of Biology, Hong Kong Baptist University

Email: jzhang@hkbu.edu.hk

We have identified two major problems with rice grain filling. The first one is the slow grain filling associated with unfavorably delayed whole plant senescence. Monocarpic plants such as rice need to initiate the whole plant senescence so that the pre-stored carbon reserve in their stem and sheath can be remobilized for the grain filling. In many cases such as heavy use of N fertilizer, strong lodging-resistant cultivars and hybrid rice associated with strong heterosis, a delayed whole plant senescence can lead to slow grain filling and unused carbon reserve in the straw at maturity. We found a properly controlled soil drying can greatly promote the whole plant senescence and therefore the grain filling. The second problem of rice grain filling is with the later-flowered inferior spikelets. Sucrose levels in these grains are actually higher than those in earlier-flowered superior spikelets but the sucrose to starch conversion is slow or inactive. Again we found proper soil drying at grain filling time can significantly improve the situation. Hormones and key gene expressions are also found to play regulative roles there.

Key words: grain filling, whole plant senescence, carbon remobilization, rice