Abstract
Drought, the most prominent threat to agricultural production worldwide, accelerates leaf senescence, leading to a decrease in canopy size, loss in photosynthesis and reduced yields. On the basis of the assumption that senescence is a type of cell death program that could be inappropriately activated during drought, we hypothesized that it may be possible to enhance drought tolerance by delaying drought-induced leaf senescence through the stress-induced synthesis of cytokinins. We generated monocot and dicot transgenic plants expressing an isopentenyltransferase gene driven by pSARK, a stress- and maturation-induced promoter. Remarkably, the suppression of drought-induced leaf senescence resulted in outstanding drought tolerance as shown by, among other responses, vigorous growth following a long drought period that killed the control plants. The transgenic plants expressing pSARK-IPT maintained high water contents and retained photosynthetic activity (albeit at a reduced level) during the drought period. A comparison of the CO2-dependent rate of photosynthesis (A/Ci curve) from wild-type and transgenic plants showed that drought severely affected the RuBP regeneration and triose phosphate use of wild type plants but not of transgenic plants. Ultrastructural analysis of leaf parenchyma cells and metabolite analysis of leaf contents indicated the occurrence of enhanced photorespiration in the pSARK-IPT trangenic plants leading to CO2 fixation under drought conditions. The transgenic plants displayed minimal yield loss when watered under reduced watering regimes of only 30% of the amount of water used under control conditions. Transgenic plants grown under reduced watering also displayed the induction of photorespiration observed under severe drought conditions. Array-based analysis indicated major expression level difference between the tolerant and wild-type plants for genes involved in photosynthesis processes localized to the chloroplasts. Some of the key genes of PSII, PSI and, ATPase complexes were strongly repressed in the wild-type stressed plants but were unaffected or marginally repressed in stressed PSARK::IPT plants. Transcript abundance of genes associated with oxidative stress tolerance and photo-protection were significantly higher in pSARK::IPT compared to wild-type plants. At the protein level, photosynthesis genes such as D1, Cyt b6, and, α-ATPase were strongly repressed only in the stressed wild-type plants. The production of drought-tolerant crops able to grow under restricted water regimes without diminution of yield would minimize drought-related losses and ensure food production in water-limited lands.Rivero RM, Shulaev V, Blumwald, E. (2009) Cytokinin-dependent photorespiration and the protection of photosynthesis during water deficit. Plant Physiol. 150:1380-1393.Rivero, RM., Kojima, M., Gepstein A., Sakakibara, H., Mittler, R., Gepstein, S., and Blumwald, E. (2007). Delayed leaf senescence induces extreme drought tolerance in a flowering plant. Proc. Natl. Acad. Sci. USA 104:19631-19636.
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Claims 13
Claim · model-written summary
Suppressing drought-induced leaf senescence gave outstanding drought tolerance, with transgenic plants growing vigorously after a long drought that killed control plants.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e1“Remarkably, the suppression of drought-induced leaf senescence resulted in outstanding drought tolerance as shown by, among other responses, vigorous growth following a long drought period that killed the control plants”
Claim · model-written summary
Transgenic pSARK-IPT plants maintained high water contents during drought.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e2“The transgenic plants expressing pSARK-IPT maintained high water contents and retained photosynthetic activity (albeit at a reduced level) during the drought period”
Claim · model-written summary
Transgenic pSARK-IPT plants retained photosynthetic activity during drought, at a reduced level.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e2“The transgenic plants expressing pSARK-IPT maintained high water contents and retained photosynthetic activity (albeit at a reduced level) during the drought period”
Claim · model-written summary
Drought severely affected RuBP regeneration and triose phosphate use in wild-type plants but not in transgenic plants.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e3“drought severely affected the RuBP regeneration and triose phosphate use of wild type plants but not of transgenic plants”
Claim · model-written summary
Enhanced photorespiration in pSARK-IPT transgenic plants may lead to CO2 fixation under drought.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e4“indicated the occurrence of enhanced photorespiration in the pSARK-IPT trangenic plants leading to CO2 fixation under drought conditions”
Claim · model-written summary
Transgenic plants under reduced watering (30% of control water) showed minimal yield loss.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e5“The transgenic plants displayed minimal yield loss when watered under reduced watering regimes of only 30% of the amount of water used under control conditions”
Claim · model-written summary
Transgenic plants under reduced watering showed induction of photorespiration.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e6“Transgenic plants grown under reduced watering also displayed the induction of photorespiration observed under severe drought conditions”
Claim · model-written summary
Array analysis showed major expression level differences between tolerant and wild-type plants for chloroplast photosynthesis genes.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e7“Array-based analysis indicated major expression level difference between the tolerant and wild-type plants for genes involved in photosynthesis processes localized to the chloroplasts”
Claim · model-written summary
Key PSII, PSI and ATPase complex genes were strongly repressed in stressed wild-type plants.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e2“Some of the key genes of PSII, PSI and, ATPase complexes were strongly repressed in the wild-type stressed plants but were unaffected or marginally repressed in stressed PSARK::IPT plants”
Claim · model-written summary
Key PSII, PSI and ATPase complex genes were unaffected or marginally repressed in stressed pSARK::IPT plants.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e2“Some of the key genes of PSII, PSI and, ATPase complexes were strongly repressed in the wild-type stressed plants but were unaffected or marginally repressed in stressed PSARK::IPT plants”
Claim · model-written summary
Transcript abundance of oxidative stress tolerance and photo-protection genes was higher in pSARK::IPT than in wild-type plants.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e2“Transcript abundance of genes associated with oxidative stress tolerance and photo-protection were significantly higher in pSARK::IPT compared to wild-type plants”
Claim · model-written summary
At protein level, D1, Cyt b6 and alpha-ATPase were strongly repressed only in stressed wild-type plants.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e2“At the protein level, photosynthesis genes such as D1, Cyt b6, and, α-ATPase were strongly repressed only in the stressed wild-type plants”
Claim · model-written summary
Drought-tolerant crops able to grow under restricted water without yield loss would minimise drought-related losses.
Verbatim
t0“Delayed leaf senescence induces extreme drought tolerance in crop plants”
e2“The production of drought-tolerant crops able to grow under restricted water regimes without diminution of yield would minimize drought-related losses”