Submitted to: Planta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/17/2007
Publication Date: 8/7/2007
Citation: Jain, M., Prasad, P., Boote, K.J., Allen Jr, L.H., Chourey, P.S. 2007. Effects of season-long high temperature growth conditions on sugar-to-starch metabolism in developing microspores of grain sorghum (Sorghum bicolor L., Moench). Planta. 227:67-79. Interpretive Summary: Previous cooperative efforts among scientists from USDA ARS, CMAVE and the University of Florida, Gainesville, led to characterization of several genes that are critical to sugar – starch pathway in developing pollen in maize and sorghum. A continuation of this coop effort has now led to this report that demonstrates: (1) sorghum plants grown in high temperature environment show reduced pollen fertility and ultimately reduced seed set (reduced crop yields) relative to plants in ambient or control environment; (2) developing pollen from the former group as compared to the latter also show altered sugar metabolism, most notably reduced starch deposition, and changes in the expression of several critical genes described in the previous study. Further characterization and eventual incorporation of such ‘heat-tolerant’ genes will provide superior germplasm that is expected to be better adapted to growth conditions associated with global warming.
Technical Abstract: High temperature stress-induced male sterility is a critical problem in grain sorghum (Sorghum bicolor L. Moench) that significantly compromises crop yields. Grain sorghum plants were grown season-long under ambient (30/20 °C, day-time maximum / night-time minimum) and high temperature (36/26 °C) conditions in sunlit Soil-Plant-Atmospheric-Research growth chambers. We report data on the effects of high temperature on sugar levels and expression profiles of genes related to sugar-to-starch metabolism in microspore populations represented by pre- and post-meiotic ‘early’ stages through post-mitotic ‘late’ stages that show detectable levels of starch deposition. Microspores from high temperature stress conditions showed starch-deficiency and considerably reduced germination, translating into 27% loss in seed-set. Sugar profiles showed significant differences in hexose levels at both ‘early’ and ‘late’ stages at the two temperature regimes; and most notably, undetectable sucrose and ~50% lower starch content in ‘late’ microspores from heat-stressed plants. Northern blot, quantitative PCR, and immunolocalization data revealed a significant reduction in the steady-state transcript abundance of Incw gene and CWI proteins in both sporophytic as well as microgametophytic tissues under high temperature conditions. Northern blot analyses also indicated greatly altered temporal expression profiles of various genes involved in sugar cleavage and utilization, transport and starch biosynthesis in heat-stressed plants. Collectively, these data suggest that impairment of CWI-mediated sucrose hydrolysis and subsequent lack of sucrose biosynthesis may be the most upstream molecular dysfunctions leading to altered carbohydrate metabolism and starch deficiency under elevated growth temperature conditions.