Two forward genetic screens for vein density mutants in sorghum converge on a cytochrome P450 gene in the brassinosteroid pathway.
The specification of vascular patterning in plants has interested plant biologists for many years. In the last decade a new context has emerged for this interest. Specifically, recent proposals to engineer C(4) traits into C(3) plants such as rice require an understanding of how the distinctive venation pattern in the leaves of C(4) plants is determined. High vein density with Kranz anatomy, whereby photosynthetic cells are arranged in encircling layers around vascular bundles, is one of the major traits that differentiate C(4) species from C(3) species. To identify genetic factors that specify C(4) leaf anatomy, we generated ethyl methanesulfonate- and γ-ray-mutagenized populations of the C(4) species sorghum (Sorghum bicolor), and screened for lines with reduced vein density. Two mutations were identified that conferred low vein density. Both mutations segregated in backcrossed F(2) populations as homozygous recessive alleles. Bulk segregant analysis using next-generation sequencing revealed that, in both cases, the mutant phenotype was associated with mutations in the CYP90D2 gene, which encodes an enzyme in the brassinosteroid biosynthesis pathway. Lack of complementation in allelism tests confirmed this result. These data indicate that the brassinosteroid pathway promotes high vein density in the sorghum leaf, and suggest that differences between C(4) and C(3) leaf anatomy may arise in part through differential activity of this pathway in the two leaf types.
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Govinda
G
Rizal
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Vivek
V
Thakur
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Jacqueline
J
Dionora
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Shanta
S
Karki
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Samart
S
Wanchana
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Kelvin
K
Acebron
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Nikki
N
Larazo
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Richard
R
Garcia
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Abigail
A
Mabilangan
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Florencia
F
Montecillo
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Florence
F
Danila
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Reychelle
R
Mogul
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Paquito
P
Pablico
Plant Breeding, Genetics, and Biotechnology Division, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.
Hei
H
Leung
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.
Jane A
JA
Langdale
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.|12 Barley Way, Marlow, SL7 2UG, UK.
John
J
Sheehy
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.
Steven
S
Kelly
C4 Rice Center, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines.|Department of Plant and Animal Sciences, University of Sheffield, Sheffield, UK.
William Paul
WP
Quick
D060406:Brassinosteroids / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D045868:Sorghum / Q000235:genetics* / Q000378:metabolism
D060406:Brassinosteroids; D010940:Plant Proteins; D003577:Cytochrome P-450 Enzyme System
C4 photosynthesis; Sorghum bicolor; brassinosteroid; gene identification; kranz anatomy; vascular patterning