Hybrid seed production in maize relies on male sterility of the female parent. This can be achieved through manual emasculation, genetic male sterility using recessive genes, or cytoplasmic genetic male sterility (CMS). CMS uses mitochondrial mutations that lead to pollen abortion and is divided into T, C, and S types distinguished by their mitochondrial DNA and proteins. The T-CMS system confers both male sterility and disease susceptibility through the T-urf13 gene. Restoration of fertility is achieved through nuclear genes and can be sporophytic or gametophytic depending on the CMS type.

1. Hybrid Seed Production and
Male sterility in Maize
Presented by
Swati
L-2011-A-52-D

2. Hybrid Seed
Inbred 1 × Inbred 2
(Female Parent) (Male Parent)
Hybrid
Different ways of inducing male sterility
I. Manual/mechanical emasculation (detasselling)
II. Genic male sterility
III. Cytoplasmic genetic male sterility
IV. Gametocides

3. Genetic Male sterility
• Male sterility determined by single recessive gene
•40 loci involved have been identified (ms1 to ms52)
• ms5 –cloned
•Problem : impossibile to maintain male sterile inbred
detasselling required

4. Conferring genetic male sterility
• Turning a critical male fertility gene inducible
• Delivering a gene encoding cytotoxic substance
fused with a male tissue specific promoter
• Antisense system

5. CMS in maize
• Three main CMS types have been described:
 CMS-T (Texas) (Rogers and Edwardson, 1952)
 CMS-C (Charrua) (Beckett, 1971)
 CMS-S (USDA) (Jones,1957)
• Distinguished by
Mitochondrial DNA restriction digestion pattern
Accumulation of mt polypeptide species assayed
by radiolabeling
Specific nuclear genes (Rf genes) that restore
pollen fertility.

6. T-cytoplasm
 Texas (T) cytoplasmic male sterility discovered in 1940s; used
extensively throughout the 1960s.
 Highly stable under all environmental conditions.
 Characterized by failure of anther exertion and pollen abortion.
 Plants bearing the T cytoplasm- susceptible to race T of the
southern corn leaf blight - (Cochliobolus heterostrophus = Bipolaris
maydis)
 Widespread use of T-cytoplasm for hybrid corn production led to
epidemic in 1970 with the widespread rise of Race T.
 Toxin produced by C. heterostrophus = T-toxin.

7. T-urf13 gene in T cytoplasm maize
Mitochondrial gene T-urf13 is a unique chimeric
sequence
• Recombination product of 5’ region of atp6 gene
and 3’ region of rrn26 gene.
• 13 kDa polypeptide is observed in T-
mitochondria, but not in N-mitochondria.

8. How does URF13 cause Cms?
Effect of URF13 protein
• Degeneration of the tapetum during microsporogenesis
• Disruption of pollen development leading to male cell
abortion
Why would mitochondrial disfunction specifically affect
pollen development?
• Mitochondrial gene functions are essential to all cells–
electron transfer, ATP formation, and translation of
mitochondrial mRNA.
• Interruption of any of these functions would be expected
to be lethal.
Confers both male sterility and disease susceptibility

9. CMS -C
• Mutations in three genes viz atp6, atp 9 and cosII-
confer CMS phenotype
CMS-S
• Sterility associated with orf355-orf77 chimeric mt
gene
• Transcripts not efficiently edited in S-cytoplasm
microspores

10. Reversion to fertility
• The reversion of CMS
strain to male fertility is
based on genetic change
• Reversion can be
spontaneous or mutagen
induced
• S-cytoplasm revert rather
frequently to male fertility
(than T & C).
Maize-CMS Restoration of fertility
system: different classes of pollen grains
are produced, but not all of them are
viable

11. C-cytoplasm
• Fertility restoration is Sporophytic
• Rf4, Rf5, Rf6 are responsible for fertility
restoration
T-cytoplasm
• Fertility restoration is sporophytic
• Rf1 (chr. 3) & Rf2(chr.9) are responsible for
fertility restoration
S-cytoplasm
• Fertility restoration is Gametophytic
• Rf3 (chr. 2) are responsible for fertility restoration
• Plasmid like element S1 & S2

12. Literature
• Skibbe D S and Schnable P S (2005) Male
sterility in Maize. Maydica 50: 367-76
• Sofi P A, Rather A G and Wani S A (2007)
Genetic and molecular basis of cytoplasmic
male sterility in maize. CBCS 2:49-60.
• Colbert T R Pioneer Hi-breed International
Patent No. US 7,049,499