Antagonistic regulation of Arabidopsis growth by brassinosteroids and abiotic stresses.
To withstand ever-changing environmental stresses, plants are equipped with phytohormone-mediated stress resistance mechanisms. Salt stress triggers abscisic acid (ABA) signaling, which enhances stress tolerance at the expense of growth. ABA is thought to inhibit the action of growth-promoting hormones, including brassinosteroids (BRs). However, the regulatory mechanisms that coordinate ABA and BR activity remain to be discovered. We noticed that ABA-treated seedlings exhibited small, round leaves and short roots, a phenotype that is characteristic of the BR signaling mutant, brassinosteroid insensitive1-9 (bri1-9). To identify genes that are antagonistically regulated by ABA and BRs, we examined published Arabidopsis microarray data sets. Of the list of genes identified, those upregulated by ABA but downregulated by BRs were enriched with a BRRE motif in their promoter sequences. After validating the microarray data using quantitative RT-PCR, we focused on RD26, which is induced by salt stress. Histochemical analysis of transgenic Arabidopsis plants expressing RD26pro:GUS revealed that the induction of GUS expression after NaCl treatment was suppressed by co-treatment with BRs, but enhanced by co-treatment with propiconazole, a BR biosynthetic inhibitor. Similarly, treatment with bikinin, an inhibitor of BIN2 kinase, not only inhibited RD26 expression, but also reduced the survival rate of the plant following exposure to salt stress. Our results suggest that ABA and BRs act antagonistically on their target genes at or after the BIN2 step in BR signaling pathways, and suggest a mechanism by which plants fine-tune their growth, particularly when stress responses and growth compete for resources.
School of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea.
Yuhee
Y
Chung
Convergence Research Center for Functional Plant Products, Advanced Institutes of Convergence Technology, Suwon 443-270, Korea.
Soon Il
SI
Kwon
School of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea ; Convergence Research Center for Functional Plant Products, Advanced Institutes of Convergence Technology, Suwon 443-270, Korea ; Plant Genomics and Breeding Institute, Seoul National University, Seoul 151-921, Korea.
Sunghwa
S
Choe
D000040:Abscisic Acid / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D060406:Brassinosteroids / Q000494:pharmacology*; D004336:Drug Antagonism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D059372:Nucleotide Motifs; D010937:Plant Growth Regulators / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D011494:Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D012965:Sodium Chloride / Q000494:pharmacology; D013312:Stress, Physiological; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics*
D000040:Abscisic Acid; D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D010937:Plant Growth Regulators; D011494:Protein Kinases; D012965:Sodium Chloride; D014157:Transcription Factors; C493887:RD26 protein, Arabidopsis; C448985:At4g18710 protein, Arabidopsis
ABA; BIN2; RD26; Root; abiotic stress; brassinosteroids