Soil bacteria augment Arabidopsis photosynthesis by decreasing glucose sensing and abscisic acid levels in planta.

Photosynthesis is regulated by environmental factors as well as endogenous sugar signals. Whereas light-driven sugar biosynthesis is essential for terrestrial organisms, as well as belowground microflora, whether and how soil symbionts regulate photosynthesis has yet to be reported. Here, we show that the plant growth-promoting soil bacterium Bacillus subtilis GB03 augments photosynthetic capacity by increasing photosynthetic efficiency and chlorophyll content in Arabidopsis. Mechanistic studies reveal an elevation of sugar accumulation as well as the suppression of classic glucose signaling responses, including hypocotyl elongation and seed germination, with exposure to GB03. Compared with wild-type plants, two Arabidopsis mutants defective in hexokinase-dependent sugar signaling exhibit increased photosynthetic capacity, which is not further enhanced with GB03 exposure. Overlap in sugar/ABA sensing is observed in GB03-exposed plants, with a reduction of ABA-biosynthetic transcripts as well as downstream metabolite levels in leaves. Moreover, exogenous ABA abrogates GB03-triggered increases in photosynthetic efficiency and chlorophyll content. These results demonstrate that certain rhizobacteria elevate photosynthesis through the modulation of endogenous sugar/ABA signaling, and establish a regulatory role for soil symbionts in plant acquisition of energy.

Overexpression of the Arabidopsis 14-3-3 protein GF14 lambda in cotton leads to a "stay-green" phenotype and improves stress tolerance under moderate drought conditions.

The Arabidopsis gene GF14 lambda that encodes a 14-3-3 protein was introduced into cotton plants to explore the physiological roles that GF14 lambda might play in plants. The expression level of GF14 lambda under the control of the cauliflower mosaic virus 35S promoter varied in transgenic cotton plants, and lines that expressed GF14 lambda demonstrated a "stay-green" phenotype and improved water-stress tolerance. These lines wilted less and maintained higher photosynthesis than segregated non-transgenic control plants under water-deficit conditions. Stomatal conductance appears to be the major factor for the observed higher photosynthetic rates under water-deficit conditions. The stomatal aperture of transgenic plants might be regulated by GF14 lambda through some transporters such as H(+)-ATPase whose activities are controlled by their interaction with 14-3-3 proteins. However, since 14-3-3 proteins interact with numerous proteins in plant cells, many metabolic processes could be affected by the GF14 lambda overexpression. Whatever the mechanisms, the traits observed in the GF14 lambda-expressing cotton plants are beneficial to crops under certain water-deficit conditions.

Predicting the extent of photosystem II photoinactivation using chlorophyll a fluorescence parameters measured during illumination.

The temperature dependence of the relationship between the decline in activity of photosystem II (PSII) and a chlorophyll a fluorescence parameter combining the excitation pressure (1-qP) and efficiency of excitation energy capture by open PSII reaction centers in the light-acclimated state (Fv'/Fm') was investigated in cotton leaves. A formula for the prediction of PSII inactivation is proposed on the basis of the results obtained. By comparison of the predicted and actual levels of PSII photoinactivation, the rate of PSII recovery was estimated from chlorophyll a fluorescence parameters measured during the day for attached cotton leaves exposed to suboptimal morning temperatures in a greenhouse.