Negative feedback regulation of auxin signaling by ATHB8/ACL5-BUD2 transcription module.
The role of auxin as main regulator of vascular differentiation is well established, and a direct correlation between the rate of xylem differentiation and the amount of auxin reaching the (pro)cambial cells has been proposed. It has been suggested that thermospermine produced by ACAULIS5 (ACL5) and bushy and dwarf2 (BUD2) is one of the factors downstream to auxin contributing to the regulation of this process in Arabidopsis. Here, we provide an in-depth characterization of the mechanism through which ACL5 modulates xylem differentiation. We show that an increased level of ACL5 slows down xylem differentiation by negatively affecting the expression of homeodomain-leucine zipper (HD-ZIP) III and key auxin signaling genes. This mechanism involves the positive regulation of thermospermine biosynthesis by the HD-ZIP III protein Arabidopsis thaliana homeobox8 tightly controlling the expression of ACL5 and BUD2. In addition, we show that the HD-ZIP III protein REVOLUTA contributes to the increased leaf vascularization and long hypocotyl phenotype of acl5 likely by a direct regulation of auxin signaling genes such as like auxin resistant2 (LAX2) and LAX3. We propose that proper formation and differentiation of xylem depend on a balance between positive and negative feedback loops operating through HD-ZIP III genes.
Food and Nutrition Research Centre, Agricultural Research Council, Via Ardeatina 546, Rome 00178, Italy.
Simona
S
Baima
Food and Nutrition Research Centre, Agricultural Research Council, Via Ardeatina 546, Rome 00178, Italy.
Valentina
V
Forte
Food and Nutrition Research Centre, Agricultural Research Council, Via Ardeatina 546, Rome 00178, Italy.
Marco
M
Possenti
Food and Nutrition Research Centre, Agricultural Research Council, Via Ardeatina 546, Rome 00178, Italy.
Andrés
A
Peñalosa
Food and Nutrition Research Centre, Agricultural Research Council, Via Ardeatina 546, Rome 00178, Italy; Present address: Department of Physics, Sapienza University of Rome, P.le A. Moro 5, 00185, Rome, Italy.
Guido
G
Leoni
Food and Nutrition Research Centre, Agricultural Research Council, Via Ardeatina 546, Rome 00178, Italy.
Sergio
S
Salvi
Food and Nutrition Research Centre, Agricultural Research Council, Via Ardeatina 546, Rome 00178, Italy; Present address: Soil-Plant System Studies Research Centre, Agricultural Research Council, Via della Navicella 2-4, 00184, Rome, Italy.
Barbara
B
Felici
Institute of Biology, Molecular Medicine and NanoBiotechnology, National Research Council, P.le A. Moro 5, Rome 00185, Italy.
Ida
I
Ruberti
Food and Nutrition Research Centre, Agricultural Research Council, Via Ardeatina 546, Rome 00178, Italy. Electronic address: giorgio.morelli@entecra.it.
Giorgio
G
Morelli
D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D007210:Indoleacetic Acids / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
C098015:ATHB-8 protein, Arabidopsis; D029681:Arabidopsis Proteins; D018398:Homeodomain Proteins; D007210:Indoleacetic Acids; D014157:Transcription Factors
Arabidopsis.; autoregulation; auxin; auxin influx transporters; procambium; thermospermine