SlCCD7 controls strigolactone biosynthesis, shoot branching and mycorrhiza-induced apocarotenoid formation in tomato.
The regulation of shoot branching is an essential determinant of plant architecture, integrating multiple external and internal signals. One of the signaling pathways regulating branching involves the MAX (more axillary branches) genes. Two of the genes within this pathway, MAX3/CCD7 and MAX4/CCD8, encode carotenoid cleavage enzymes involved in generating a branch-inhibiting hormone, recently identified as strigolactone. Here, we report the cloning of SlCCD7 from tomato. As in other species, SlCCD7 encodes an enzyme capable of cleaving cyclic and acyclic carotenoids. However, the SlCCD7 protein has 30 additional amino acids of unknown function at its C terminus. Tomato plants expressing a SlCCD7 antisense construct display greatly increased branching. To reveal the underlying changes of this strong physiological phenotype, a metabolomic screen was conducted. With the exception of a reduction of stem amino acid content in the transgenic lines, no major changes were observed. In contrast, targeted analysis of the same plants revealed significantly decreased levels of strigolactone. There were no significant changes in root carotenoids, indicating that relatively little substrate is required to produce the bioactive strigolactones. The germination rate of Orobanche ramosa seeds was reduced by up to 90% on application of extract from the SlCCD7 antisense lines, compared with the wild type. Additionally, upon mycorrhizal colonization, C(13) cyclohexenone and C(14) mycorradicin apocarotenoid levels were greatly reduced in the roots of the antisense lines, implicating SlCCD7 in their biosynthesis. This work demonstrates the diverse roles of MAX3/CCD7 in strigolactone production, shoot branching, source-sink interactions and production of arbuscular mycorrhiza-induced apocarotenoids.
Horticultural Sciences Department and the Plant Molecular & Cellular Biology Program, University of Florida, Gainesville, Florida 32611, USA.
Jonathan T
JT
Vogel
Michael H
MH
Walter
Patrick
P
Giavalisco
Anna
A
Lytovchenko
Wouter
W
Kohlen
Tatsiana
T
Charnikhova
Andrew J
AJ
Simkin
Charles
C
Goulet
Dieter
D
Strack
Harro J
HJ
Bouwmeester
Alisdair R
AR
Fernie
Harry J
HJ
Klee
D000595:Amino Acid Sequence; D002338:Carotenoids / Q000096:biosynthesis*; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D003998:Dicarboxylic Acids / Q000378:metabolism; D049308:Dioxygenases / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D054884:Host-Pathogen Interactions; D007783:Lactones / Q000378:metabolism*; D018551:Solanum lycopersicum / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology; D008969:Molecular Sequence Data; D009154:Mutation; D038821:Mycorrhizae / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000382:microbiology; D018520:Plant Shoots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D011090:Polyenes / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
D003998:Dicarboxylic Acids; D007783:Lactones; D010940:Plant Proteins; D011090:Polyenes; C458517:mycorradicin; D002338:Carotenoids; D049308:Dioxygenases