Inflorescence development:
the basis of maize productivity
Paula McSteen
Division of Biological Sciences
Bond Life Sciences Center
University of Missouri-Columbia
Overview
Inflorescence development
Genetic analysis of inflorescence
development – the role of auxin
Hormonal and environmental control of
ear shoot formation
tassel =
male inflorescence
ear =
female inflorescence
McSteen et al 2000 TIPS 5: 61-66
Maize has separate male and
female inflorescences
spikelet pair
floret pair
tassel
Tassel inflorescence
mature ear
ear shoot
Ear inflorescence
root apical meristem
shoot apical meristem
axillary meristem
Meristems control development
Tsiantis and Hay 2003 Nature Reviews Genetics 4:169-180
Vegetative to floral transition
- leaves to flowers
McSteen et al 2000 TIPS 5: 61-66
Vegetative
meristem
Inflorescence
meristem
Transition
stage
Inflorescence meristem
Maize inflorescence development
– transition stage
X Wu and P McSteen, unpublished
0.5mm
IM
Maize inflorescence development
– branch meristem
1.0mm
X Wu and P McSteen, unpublished
BM
spikelet pair meristem
Maize inflorescence development
- spikelet pair meristem
2.0mm
X Wu and P McSteen, unpublished
SPM
spikelet pair meristem
spikelet meristem
Maize inflorescence development
- spikelet meristem
3.5mm
X Wu and P McSteen, unpublished
SPM
SM
spikelet pair meristem
spikelet meristem
Maize inflorescence development
- second spikelet meristem
5.0mm
S Barazesh and P McSteen, unpublished
SM
Spikelet pair meristem
Spikelet meristem
Maize inflorescence development
- apical meristem collapse
6.0mm
K Phillips and P McSteen, unpublished
Spikelet pair meristem
Spikelet meristem
Maize inflorescence development
- floral meristem
Floral meristem
8.5mm
X Wu and P McSteen, unpublished
FM
Spikelet pair meristem
Spikelet meristem
Floral meristem
Maize inflorescence development
- second floral meristem
11mm
X Wu and P McSteen, unpublished
Tassel and ear – similar development
Tassel
Ear
Phillips et al 2011 Plant Cell, in press
IM
SPM
SM
BM
IM
SPM
SM
FM
Sex determination occurs later
adapted from Veit et al 1983 Plant Cell 5:1205-1215
Summary of development
BM, SPM, SM, FM = axillary meristems
Ear shoot, tiller bud = axillary meristems
Tassel and ear have similar development
Overview
Inflorescence development
Genetic analysis of inflorescence
development – the role of auxin
Hormonal and environmental control of
ear shoot formation
Genetic analysis of
inflorescence development
auxin biosynthesis –
vanishing tassel2 (vt2)
auxin transport –
barren inflorescence2 (bif2)
auxin response –
barren stalk1 (ba1)
bif2 mutants make fewer branches
Normal
bif2
McSteen et al 2001 Development 128:2881-2891
bif2 mutants make fewer kernels
Normal
bif2
bif2 fails to produce axillary meristems
Normal
bif2
SPM
IM
bif2 is required for initiation
of all axillary meristems
in maize
McSteen et al 2001 Development 128:2881-2891
McSteen et al 2007 Plant Physiology 144:1000-1011
McSteen et al 2007 Plant Physiology 144:1000-1011
bif2 encodes a serine/threonine
protein kinase
Model for BIF2 function
BIF2
P
Cell
membrane
Promoter
BA1 targets
IAA
Nucleus
BIF2
P
P
BIF2
P
P
BA1
P
ZmPDK
P
Auxin
transport
Axillary
meristem
initiation
Skirpan et al 2008 Plant J 55:787-797
Skirpan et al 2009 Plant Cell Physiol 50:652-657
Genetic analysis of
inflorescence development
auxin biosynthesis –
vanishing tassel2 (vt2)
auxin transport –
barren inflorescence2 (bif2)
auxin response –
barren stalk1 (ba1)
vt2 affects inflorescence development
Normal
vt2
vt2
Normal
Phillips et al 2011 Plant Cell in press
vt2 mutants fail to produce
axillary meristems
Normal
vt2
AM
IM
SPM
IM
TRP
IAM
IAOx
IPA
TAM
IAN
IAAld
HTAM
IAA
Four tryptophan-dependent auxin
biosynthesis pathways are proposed
spi1
vt2
Phillips et al 2011 Plant Cell in press
Auxin is required for initiation
of all axillary meristems
in maize
McSteen et al 2007 Plant Physiology 144:1000-1011
Wu and McSteen 2007 Am J Bot 94: 1745-1755
Gallavotti et al 2008 PNAS 105:15196-15201
Skirpan et al 2009 Plant Cell Physiol 50:652-657
Phillips et al 2011 Plant Cell in press
Overview
Inflorescence development
Genetic analysis of inflorescence
development – the role of auxin
Hormonal and environmental control of
ear shoot formation
Hormonal and environmental control
of ear shoot formation
initiation - auxin
outgrowth - hormones, density, fertilizer
maintenance - cytokinin, thiamine, boron
Auxin mutants have defects in
ear shoot initiation
0
0.5
1
1.5
2
wt
vt2
Ear shoot N
umber
2.0
1.0
0.0
1.5
0.5
+/+
vt2/vt2
Phillips et al 2011 Plant Cell in press
ba1 and
ba2 mutants lack ear shoots
Normal ba2
Normal
ba2
Skirpan and McSteen, unpublished
Normal
ba1
Gallavotti et al 2004 Nature 432:630-635
N ba2
Hormonal and environmental control
of ear shoot formation
initiation - auxin
outgrowth - hormones, density, fertilizer
maintenance - cytokinin, thiamine, boron
bud
root
shoot
leaf
IAA
strigol
CK
McSteen 2009 Plant Physiology 149:46-55
Hormonal factors
impacting bud outgrowth
Auxin regulates tillering in rice
Xu et al 2005 Plant Cell Physiol 46:1674-1681
wildtype rice
OsPIN1 mutant
shade
low R/FR
fertilizer
bud
density
root
shoot
leaf
IAA
strigol
CK
McSteen 2009 Plant Physiology 149:46-55
Environmental factors
impacting bud outgrowth
Kebrom and Brutnell 2007 J Exp Bot 58:3079-3089
Light regulates tiller production
in sorghum
phyB
mutant
wildtype
sorghum
tb1 regulates tillering in maize
Normal maize
tb1 mutant
Hubbard et al 2002 Genetics 162: 1927-1935
Hormonal and environmental control
of ear shoot formation
initiation - auxin
outgrowth - hormones, density, fertilizer
maintenance - cytokinin, thiamine, boron
Thiamine deficiency results in defects
in apical meristem maintenance
Woodward et al 2010 Plant Cell 22:3305-3317
Conclusions
multiple hormonal and environmental
impacts on ear formation
important to know the stage affected to
understand the mechanisms involved
similar mechanisms of regulation of all
axillary structures
Acknowledgements
PSU lab
Andrea Skirpan
Solmaz Barazesh
Xianting Wu
Kim Phillips
MU lab
Hong Yao
Amanda Durbak
Laura Matera
Collaborators
Andrea Gallavotti, UCSD
Bob Schmidt, UCSD
Yunde Zhao, UCSD
Simon Malcomber, CSULB
David Jackson, CSHL
Jerry Cohen, U Minnesota
Mike Scanlon, Cornell
Funding
NSF –
bif2, AuxinEvoDevo
USDA –
spi1, vt2
