Tackling drought stress: receptor-like kinases present new approaches

Abstract

Global climate change and a growing population require tackling the reduction in arable land and improving biomass production and seed yield per area under varying conditions. One of these conditions is suboptimal water availability. Here, we review some of the classical approaches to dealing with plant response to drought stress and we evaluate how research on RECEPTOR-LIKE KINASES (RLKs) can contribute to improving plant performance under drought stress. RLKs are considered as key regulators of plant architecture and growth behavior, but they also function in defense and stress responses. The available literature and analyses of available transcript profiling data indeed suggest that RLKs can play an important role in optimizing plant responses to drought stress. In addition, RLK pathways are ideal targets for nontransgenic approaches, such as synthetic molecules, providing a novel strategy to manipulate their activity and supporting translational studies from model species, such as Arabidopsis thaliana, to economically useful crops.

Figure 1.

Impact of Water Depletion on Leaf Development and Rate of Photosynthesis. (A) Two leaf surfaces of the maize inbred line B73 are shown at the same developmental stage. The left leaf of a daily watered plant is fully expanded. The leaf at the right from a plant that was depleted of water for 10 d contains a smaller leaf surface area and less chlorophyll, stomata are closed, and leaf margins are curled to avoid water loss. Watering of plants at this stage leads to full recovery. (B) Soil moisture continuously decreases after water depletion. Below a critical moisture of ∼15% (4th to 5th day after water depletion) rates of photosynthesis and transpiration drop dramatically to ∼10% of well-watered rates. (Figure courtesy of Manfred Gahrtz.)

Figure 2.

Screen for Differentially Expressed RLK Genes in Arabidopsis. Data were taken from a drought stress time series across root (A) and shoot (B) tissues (AtGenExpress; Kilian et al., 2007). In addition, data from a mannitol treatment for corresponding RLKs is shown (Skirycz et al., 2011a). Kilian et al. (2007) applied drought stress as follows: The plants were exposed to a stream of air in a clean bench for 15 min, which resulted in a loss of 10% of the plant’s fresh weight. Subsequently, plants were returned to the growth chamber and harvested at indicated time intervals. Skirycz et al. (2011a) used an experimental setup that reproducibly reduced the leaf area by ∼50%. Seedlings 9 d after stratification were transferred to 25 mM mannitol-containing medium (decreasing the water potential of the medium and, hence, water uptake of the exposed roots), and leaf primordia were harvested at indicated time intervals. The AtGenExpress drought microarray data set (Kilian et al., 2007) was downloaded from NASCArrays (Craigon et al., 2004) and then RMA normalized and analyzed using Bioconductor (Gentleman et al., 2004), which generated log₂-fold changes across all of the probes. This list was filtered for 610 RLK family members (Shiu and Bleecker, 2001a). Blocks represent twofold upregulated (red), 1.5-fold upregulated (orange), twofold downregulated (blue), and 1.5-fold downregulated genes (light blue) in drought stress relative to control tissue. Asterisks indicate RLKs investigated by ten Hove et al. (2011), with T-DNA mutants displaying salt stress resistance.

Figure 3.

Early Effect of Drought on RLK Expression. Number of RLK genes identified as candidates for differential expression within 24 h of onset of drought stress. Data from the AtGenExpress drought microarray data set (Kilian et al., 2007) at the time points 0.25 to 24 h for root (A) and shoot (B). Putative differential expression is defined as twofold or greater change in expression in drought stress relative to control tissue. Red and blue lines represent the number of upregulated and downregulated RLK genes, respectively. There is a large spike in upregulated gene numbers at the 1-h time point in the root and at the 0.5-h time point in shoot.