Background Short episodes of high temperature (HT) stress during reproductive stages of development cause significant yield losses in wheat (Triticum aestivum L.). Two independent experiments were conducted to quantify the effects of HT during anthesis and grain filling periods on photosynthesis, leaf lipidome, and yield traits in wheat. In experiment I, wheat genotype Seri82 was exposed to optimum temperature (OT; 22/14 °C; day/night) or HT (32/22 °C) for 14 d during anthesis stage. In experiment II, the plants were exposed to OT or HT for 14 d during the grain filling stage. During the HT stress, chlorophyll index, thylakoid membrane damage, stomatal conductance, photosynthetic rate and leaf lipid composition were measured. At maturity, grain yield and its components were quantified. Results HT stress during anthesis or grain filling stage decreased photosynthetic rate (17 and 25%, respectively) and grain yield plant− 1 (29 and 44%, respectively), and increased thylakoid membrane damage (61 and 68%, respectively) compared to their respective control (OT). HT stress during anthesis or grain filling stage increased the molar percentage of less unsaturated lipid species [36:5- monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG)]. However, at grain filling stage, HT stress decreased the molar percentage of more unsaturated lipid species (36:6- MGDG and DGDG). There was a significant positive relationship between photosynthetic rate and grain yield plant− 1, and a negative relationship between thylakoid membrane damage and photosynthetic rate. Conclusions The study suggests that maintaining thylakoid membrane stability, and seed-set per cent and individual grain weight under HT stress can improve the photosynthetic rate and grain yield, respectively.

Background : Short episodes of high temperature (HT) stress during reproductive stages of development cause significant yield losses in wheat ( Triticum aestivum L.). Two independent experiments were conducted to quantify the effects of high temperature (HT) during anthesis and grain filling periods on photosynthesis, leaf lipidome, and yield traits in wheat. In experiment I, wheat genotype Seri82 was exposed to optimum temperature (OT; 22/14 °C; day/night) or HT (32/22 °C) for 14 d during anthesis stage. In experiment II, the plants were exposed to OT or HT for 14 d during grain filling stage. During the HT stress, chlorophyll index, thylakoid membrane damage, stomatal conductance, photosynthetic rate and leaf lipid composition were measured. At maturity, grain yield and its components were quantified. Results : HT stress during anthesis or grain filling stage decreased photosynthetic rate (17 and 25%, respectively) and grain yield plant -1 (29 and 44%, respectively), and increased thylakoid membrane damage (61 and 68%, respectively) compared to their respective control (OT). HT stress during anthesis or grain filling stage increased the levels of less unsaturated lipid species [36:5- monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG)]. However, at grain filling stage, HT stress decreased the levels of more unsaturated lipid species (36:6- MGDG and DGDG). There was a significant positive relationship between photosynthetic rate and grain yield plant -1 , and a negative relationship between thylakoid membrane damage and photosynthetic rate. Conclusions : The study suggests that maintaining thylakoid membrane stability, and seed-set percent and individual grain weight under HT stress can improve photosynthetic rate and grain yield, respectively.

Heat Shock Protein 101 (HSP101), the homolog of Caseinolytic Protease B (CLPB) proteins, has functional conservation across species to play roles in heat acclimation and plant development. In wheat, several TaHSP101/CLPB genes were identified, but have not been comprehensively characterized. Given the complexity of a polyploid genome with its phenomena of homoeologous expression bias, detailed analysis on the whole TaCLPB family members is important to understand the genetic basis of heat tolerance in hexaploid wheat. In this study, a genome-wide analysis revealed thirteen members of TaCLPB gene family and their expression patterns in various tissues, developmental stages, and stress conditions. Detailed characterization of TaCLPB gene and protein structures suggested potential variations of the sub-cellular localization and their functional regulations. We revealed homoeologous specific variations among TaCLPB gene copies that have not been reported earlier. A study of the Chromosome 1 TaCLPB in four wheat genotypes demonstrated unique patterns of the homoeologous gene expression under moderate and extreme heat treatments. The results give insight into the strategies to improve heat tolerance by targeting one or some of the TaCLPB genes in wheat.

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OsHox-6, belongs to the transcription factor homeodomain leucine zipper (HD-Zip) protein sub-family I, has unknown function. This study was aimed to characterize the phenotypes of two homozygous transgenic rice lines (S29-62-2 and S.40.4-158-1) containing an extra copy of OsHox-6 gene under the control of a rice constitutive promoter, OsLEA3, and to evaluate their tolerance to water stress. A real-time quantitative PCR (qRT-PCR) showed that the transcript expression of OsHox-6 gene in the transgenic lines increased 5-10 folds under a normal irrigation and 10-20 folds after exposure to water stress conditions as compared to its wild type control. Transgenic plants overexpressing OsHox-6 exhibited phenotypic alteration at the normal irrigation by inducing tiller formation, suggesting a decrease in the apical dominance. Transgenic plants also showed significant enhancement in the total grain number, however, the number of empty grains  also increased significantly (~16-22%).  After imposed to the water stress, the number of empty grains in the transgenic lines was even higher (up to 83% in average). Furthermore, observations on the water loss rates, relative water contents and drought resistance indices (DRI) suggested that the overexpression of OsHox-6 did not significantly increase tolerance to water stress.  Further research is required to reveal the detailed mechanisms of OsHox-6 in response to water and other abiotic stresses.