Genetic Dissection of Ambient Temperature Signaling in Plants

The year 2016 just surpassed 2015 and 2014 as the warmest year ever recorded since
systematic temperature measurements began more than a century ago in 1880. The year 2015
saw the toppling of several symbolic mileposts: notably, it was 1.0°C warmer than preindustrial
times, and the Mauna Loa observatory recorded its first annual mean carbon dioxide
concentration greater than 400 ppm (American Meteorological Society, 2016). The fifth report of
the Intergovernmental Panel on Climate Change projects an increase of 0.8–4.8 °C in global
mean surface temperature within the twenty-first century (IPCC, 2013). As such, global climate
change poses a significant threat to biodiversity in general, and with regard to this proposal
especially to plant growth and productivity. From an agricultural point of view, crop performance
is predicted to suffer greatly due to global warming and associated effects such as water
availability (Battisti et al., 2009), while food production is required to increase significantly to
sustain a growing and more demanding world population. A meta-analysis summarizing more
than 1,700 studies on the effects of climate change and adaptations on crop yields revealed a
consensus that in the second half of this century, climate warming is likely to have a negative
effect on yields of important staple crops (Challinor et al., 2013). In fact, experimental and crop-
based models for major grains show direct yield losses in the range of 2.5 to 16% for every 1°C
increase in seasonal temperature (Peng et al., 2004; Lobell et al., 2008). Another meta-study
demonstrated that already today global warming is negatively affecting crop yields. Between
1980 and 2008 world-wide warming caused, for example, global wheat production to decline by
5.5 % (relative to a counterfactual without climate trends) (Lobell et al., 2011). Based on these
predictions, it seems useful to generate a basic understanding of what increased ambient
temperatures cause on a developmental and physiological level.
From a developmental perspective, even a moderate increase in ambient temperature functions
as an environmental stimulus that impacts on virtually all growth and developmental programs.
Elongation of hypocotyls, petioles and roots as well as hyponastic movements of cotyledons
and leaves are some of the earliest thermomorphogenic effects across Arabidopsis thaliana
accessions in response to high ambient temperature (Ibanez et al., 2017). The resulting open rosette structure is suggested to move the sensitive meristematic and photosynthetically active tissues away from heat-absorbing soil and promote cooling by allowing better access to moving air. Plants which show this reprogramming of growth in response to high ambient temperature exhibit greater transpiration rates and cooler leaves than plants which lack these adaptive growth phenotypes. Thus, such acclimation may contribute to high temperature mitigation by enhancing leaf evaporative cooling. In addition, plants grown at high temperature have fewer stomata and develop smaller and thinner leaves which may further assist cooling by reducing boundary-layer thickness and stimulating heat dissipation by evaporation and convection (reviewed in Quint et al., 2016). The suite of morphological changes that contribute to adaptive growth acclimation to otherwise detrimental high ambient temperature conditions are collectively called thermomorphogenesis (Erwin et al.,1989; Quint et al., 2016). A prerequisite for the adaptation of crops to globally increasing temperatures is a fundamental understanding of how the plant senses temperature and translates temperature stimuli into growth responses. As such, it is imperative to elucidate the signal transduction cascade triggered by temperature stimuli. As in various other fields that have meanwhile found their way into breeding programs (flowering time, etc.), the preferred system for genetic dissection of thermomorphogenesis signaling is the plant model organism A. thaliana. In most cases,signaling components are conserved within the flowering plants and at least in part retain their function also across the eudicot-monocot clades.
This project is a follow-up proposal for a second funding period of the project entitled ‘Genetic
dissection of signaling processes regulating response to elevated ambient temperatures
in Arabidopsis thaliana’ (Qu 141/3-1).
The objectives of the previous proposal were as outlined below:
i) Identification of genes involved in responses to moderately increased ambient temperatures.
ii) Detailed molecular and physiological characterization of novel players in various temperature-induced adaptation responses.
iii) First genetic dissection of a plant ghost QTL and the identification of the causative genes.
The aims of objectives i and ii were fully achieved. For objective iii, we were able to clone and complement one of the two loci underlying the mentioned QTL.

The proposed work packages (WPs) in the follow-up proposal are directly connected to the results generated in the first funding period and therefore represent a straight-forward continuation. The project can be separated into two independent WPs. In brief, WP1 picks up the sequenced but yet to be cloned mutants that were identified in the first period. This approach will allow to identify potentially novel components in the regulation of temperature responses. WP2 will focus specifically on the mechanisms involved in the regulation of transcriptional temperature responses.