Abstract
Plant cis-elements play important roles in global regulation of gene expression. Based on microarray data from rice flag leaves during early senescence, we identified W-box and G-box cis-elements as positive regulators of senescence in the important rice variety Minghui 63. Both cis-elements were bound by leaf senescence-specific proteins in vitro and influenced senescence in vivo. Furthermore, combination of the two elements drove enhanced expression during leaf senescence, and copy numbers of the cis-elements significantly affected the levels of expression. The W-box is the cognate cis-element for WRKY proteins, while the G-box is the cognate cis-element for bZIP, bHLH and NAC proteins. Consistent with this, WRKY, bZIP, bHLH and NAC family members were overrepresented among transcription factor genes up-regulated according during senescence. Crosstalk between ABA, CTK, BR, auxin, GA and JA during senescence was uncovered by comparing expression patterns of senescence up-regulated transcription factors. Together, our results indicate that hormone-mediated signaling could converge on leaf senescence at the transcriptional level through W-box and G-box elements. Considering that there are very few documented early senescence-related cis-elements, our results significantly contribute to understanding the regulation of flag leaf senescence and provide prioritized targets for stay-green trait improvement.
Highlights
The expression patterns of several senescence-associated genes is induced at the onset of leaf senescence, and we monitored those genes to examine the flag leaf senescence process at 1, 5, 10, 15, 20 and 25 daf
Among the transcription factors (TFs) families overrepresented in our set of differentially regulated genes, we focused on WRKY, bZIP, bHLH and NAC families
Applying a novel bioinformatics algorithm, we here demonstrated on a genome-wide scale that W-box and G-box elements are significantly enriched in promoters of early senescence-inducible genes in rice flag leaf
Summary
Expression of OsTZF1, a member of the CCCH-type zinc finger gene family in rice, is induced by multiple factors including drought, high-salt stress, hydrogen peroxide (H2O2), ABA, JA and salicylic acid (SA). Consistent with these findings, rice plants in which overexpression of OsTZF1 is driven by a maize (Zea mays) ubiquitin promoter show pleiotropic phenotypes including delayed seed germination, growth retardation at the seedling stage, delayed leaf senescence, improved tolerance to high-salt and drought stresses, whereas OsTZF1 knock-down plants exhibit much the opposite phenotypes[13]. Understanding the mechanism of flag leaf senescence and elucidating the regulatory network between the signaling pathways is essential for the improvement of grain yield. The identification of functional cis-elements may contribute to the improvement of the stay-green phenotype in plants
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