Feeling the heat: developmental and molecular responses of wheat and barley to high ambient temperatures

Abstract

The increasing demand for global food security in the face of a warming climate is leading researchers to investigate the physiological and molecular responses of cereals to rising ambient temperatures. Wheat and barley are temperate cereals whose yields are adversely affected by high ambient temperatures, with each 1 °C increase above optimum temperatures reducing productivity by 5-6%. Reproductive development is vulnerable to high-temperature stress, which reduces yields by decreasing grain number and/or size and weight. In recent years, analysis of early inflorescence development and genetic pathways that control the vegetative to floral transition have elucidated molecular processes that respond to rising temperatures, including those involved in the vernalization- and photoperiod-dependent control of flowering. In comparison, our understanding of genes that underpin thermal responses during later developmental stages remains poor, thus highlighting a key area for future research. This review outlines the responses of developmental genes to warmer conditions and summarizes our knowledge of the reproductive traits of wheat and barley influenced by high temperatures. We explore ways in which recent advances in wheat and barley research capabilities could help identify genes that underpin responses to rising temperatures, and how improved knowledge of the genetic regulation of reproduction and plant architecture could be used to develop thermally resilient cultivars.

Keywords: Barley; cereals; high temperature; reproductive development; thermal resilience; wheat.

Fig. 1.

Optimum and maximum temperatures for the reproductive growth stages in wheat. Optimum temperatures are in green, and maximum temperatures (temperatures higher than which are damaging) are in red for key developmental stages of wheat and barley that are vulnerable to high temperatures. Insert images show a double ridge apex, terminal spikelet apex, prophase I meiotic cell with DAP1 (blue) and TaASY1 (red), and grain at maturity (from left to right). The respective Zadoks (Z; Zadoks et al., 1974) and Waddington (W; Waddington et al., 1983) scales for each growth stage are indicated.

Fig. 2.

Thermally responsive components of the floral promoting pathway in wheat and barley. Schematic illustrating the interactions between FT1, VRN1, VRN2, ODDSOC2, PPD1, ELF3, and LUX, with their reported interactions with high growth temperatures. Boxes indicate genes that are photoperiod dependent, circadian clock regulated, and vernalization responsive. Green arrows indicate up-regulated genes and red arrows indicate down-regulated genes during exposure to high temperatures.