Stress-Induced Cytokinin Synthesis Increases Drought Tolerance through the Coordinated Regulation of Carbon and Nitrogen Assimilation in Rice

Abstract

The effects of water deficit on carbon and nitrogen metabolism were investigated in flag leaves of wild-type and transgenic rice (Oryza sativa japonica 'Kitaake') plants expressing ISOPENTENYLTRANSFERASE (IPT; encoding the enzyme that mediates the rate-limiting step in cytokinin synthesis) under the control of P SARK , a maturation-and stress-induced promoter. While the wildtype plants displayed inhibition of photosynthesis and nitrogen assimilation during water stress, neither carbon nor nitrogen assimilation was affected by stress in the transgenic P SARK ::IPT plants. In the transgenic plants, photosynthesis was maintained at control levels during stress and the flag leaf showed increased sucrose (Suc) phosphate synthase activity and reduced Suc synthase and invertase activities, leading to increased Suc contents. The sustained carbon assimilation in the transgenic P SARK ::IPT plants was well correlated with enhanced nitrate content, higher nitrate reductase activity, and sustained ammonium contents, indicating that the stress-induced cytokinin synthesis in the transgenic plants played a role in maintaining nitrate acquisition. Protein contents decreased and free amino acids increased in wild-type plants during stress, while protein content was preserved in the transgenic plants. Our results indicate that the stress-induced cytokinin synthesis in the transgenic plants promoted sink strengthening through a cytokinin-dependent coordinated regulation of carbon and nitrogen metabolism that facilitates an enhanced tolerance of the transgenic plants to water deficit.

The rice transcription factor OsWRKY47 is a positive regulator of the response to water deficit stress

“…Among these, the CKinduced delayed senescence has been shown to be effective in increasing the tolerance of plants to water deficit (Rivero et al 2007). Transgenic plants expressing the IPT gene, encoding a key enzyme in CK synthesis, under the control of SARK (a stress-and maturity-induced promoter) displayed enhanced photosynthesis and high yields under water stress (Rivero et al 2007;Peleg et al 2011b;Reguera et al 2013). A Gene expression profile of flag leaves from wild-type plants and transgenic rice plants expressing P SARK ::IPT, highlighted the differential expression of OsWRKY47 in the P SARK ::IPT plants under water stress (Peleg et al 2011b).…”

Stress-Induced Chloroplast Degradation in Arabidopsis Is Regulated via a Process Independent of Autophagy and Senescence-Associated Vacuoles

“…It has been shown previously that the cytokinin-dependent inhibition of droughtinduced senescence resulted in sustained photosynthetic activity during the stress episode and that it enhanced tolerance to water deficit (Rivero et al, 2007(Rivero et al, , 2009(Rivero et al, , 2010. The expression of isopentenyl synthase (IPT), encoding a key enzyme in cytokinin synthesis, under the control of a maturation-and stress-induced promoter (pSARK) leads to the protection of the photosynthetic apparatus and enhanced chloroplast stability (Rivero et al, 2010;Reguera et al, 2013). Using DNA microarrays, we analyzed RNA expression patterns in wild-type and transgenic pSARK-IPT rice (Oryza sativa) plants during water deficit (Peleg et al, 2011;Reguera et al, 2013).…”

“…The expression of isopentenyl synthase (IPT), encoding a key enzyme in cytokinin synthesis, under the control of a maturation-and stress-induced promoter (pSARK) leads to the protection of the photosynthetic apparatus and enhanced chloroplast stability (Rivero et al, 2010;Reguera et al, 2013). Using DNA microarrays, we analyzed RNA expression patterns in wild-type and transgenic pSARK-IPT rice (Oryza sativa) plants during water deficit (Peleg et al, 2011;Reguera et al, 2013). The expression of one gene encoding a chloroplast protein with unknown function (LOC_Os05g49940) was activated by stress in the wild-type plants but not in the transgenic pSARK-IPT plants (Peleg et al, 2011).…”

Physiological, phenometric and productive changes in soybean crop due to the use of kinetin

“…This characteristic was observed in rice plants exhibiting overexpression of the ipt gene (which encodes cytokinin synthesis). Under water stress, these plants exhibited a 3-fold increase in the nitrate reductase activity, when compared to wild plants (Reguera et al 2013).…”