Abscisic acid regulates axillary bud outgrowth responses to the ratio of red to far-red light.
Low red light/far-red light ratio (R:FR) serves as an indicator of impending competition and has been demonstrated to suppress branch development. The regulation of Arabidopsis (Arabidopsis thaliana) rosette bud outgrowth by the R:FR and the associated mechanisms were investigated at several levels. Growth under low R:FR suppressed outgrowth of the third from topmost bud (bud n-2) but not that of the topmost bud. Subsequently increasing the R:FR near the time of anthesis promoted bud n-2 outgrowth and reduced topmost bud growth. Buds from specific rosette positions, exhibiting divergent fates to increased R:FR, were harvested 3 h after modifying the R:FR and were used to conduct ATH1 microarray-based transcriptome profiling. Differentially expressed genes showed enrichment of light signaling and hormone-related Gene Ontology terms and promoter motifs, most notably those associated with abscisic acid (ABA). Genes associated with ABA biosynthesis, including the key biosynthetic gene NINE-CIS-EPOXYCAROTENOID DIOXYGENASE3 (NCED3), and with ABA signaling were expressed at higher levels in the responsive bud n-2, and increasing the R:FR decreased their expression only in bud n-2. ABA abundance in responsive buds decreased within 12 h of increasing the R:FR, while indole-3-acetic acid levels did not change. A role for ABA in repressing bud outgrowth from lower positions under low R:FR was demonstrated using the nced3-2 and aba2-1 ABA biosynthesis mutants, which showed enhanced branching and a defective bud n-2 outgrowth response to low R:FR. The results provide evidence that ABA regulates bud outgrowth responses to the R:FR and thus extend the known hormonal pathways associated with the regulation of branching and shade avoidance.
Department of Soil and Crop Sciences, Texas A&M University and Texas A&M AgriLife Research, College Station, Texas 77843.
Srirama Krishna
SK
Reddy
Srinidhi V
SV
Holalu
Jorge J
JJ
Casal
Scott A
SA
Finlayson
D000040:Abscisic Acid / Q000096:biosynthesis / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D053898:Biosynthetic Pathways / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D060146:Ecotype; D035264:Flowers / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000528:radiation effects*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000528:radiation effects; D063990:Gene Ontology; D017343:Genes, Plant / Q000235:genetics; D007210:Indoleacetic Acids / Q000378:metabolism; D008027:Light; D055537:Light Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D010641:Phenotype
D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; C030737:indoleacetic acid; D000040:Abscisic Acid