Luis Felipe P' Silva

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Prospection of Genes of Interest in Agriculture

• Luis Felipe P. Silva

Laboratory of Functional Genomics College of
Veterinary Medicine and Animal Science Universidad
e de São Paulo Pirassununga
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Mission

• Elucidate physiological pathways hindering cattle
  productivity in Brazil
• Areas of current research
• Sexual maturation of Zebu heifers
• Role of leptin on attainment of puberty
• Nutritional quality of tropical forages
• Maize silage
• Guineagrass

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Understanding nutritional quality of forages

• Forages form the basis for cattle production in
  Brazil
• 170 mi ha (76 of agricultural land)
• 95 of beef are raised exclusively on pasture
• Guineagrass and Brachiaria respond for more than
  85 of forage area

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Understanding nutritional quality of forages

• Digestibility of tropical forages is low and
  decreases rapidly with advanced maturity

Source Muir Jank (2004)
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Understanding nutritional quality of forages

• On average, tropical forages are 15 less
  digestible than temperate forages
• C4 plants (Kranz anatomy - lignification)
• Protective structures (lignification)
• Long warm nights (lignification)
• An increase in 10 of NDF digestibility would
  results in additional 1.6 million tons of carcass
  in Brazil (US 3.5 billions/year)

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Forage breeding

• Cattle production depends heavily on
  forage production
• Forage quality is low and declines rapidly with
  maturity
• 90 mi ha of cultivated forages (ABRASEM)
• 100,000 t of seeds per year
• US 100 mi per year

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Forage breeding

• How many cultivars were released in Brazil as a
  results of a forage breeding program?
• None
• Two from Colombia (CIAT)
• Tropical forages are apomitic
• Release of cultivars by
  selection of accessions
  rather than breeding

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Metabolic engineering
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Characterization of genes related to
lignification in guineagrass

• Objectives
• To sequence mRNA coding for the main enzymes in
  the lignin synthesis pathway
• Study the effect of maturity on expression of
  these genes
• Identify genes strongly correlated with the
  digestibility decline with advanced maturity

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Material and Methods

• Field study of 12 P. maximum accessions in Campo
  Grande, MS (20.25S, 54.40W).
• Plots of 4 x 2.5 m with 6 lines.
• After leveling cut on December 29th of 2005,
  plots were fertilized and harvested with 30, 60
  or 90 days of regrowth.

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Material and Methods

• At each date two lines were harvested
• Total mass was weighted and sub-sampled for
  determining leafstem ratio and senescent
  material
• Stem stalk leaf sheath
• Leaf leaf blade
• Dried at 55oC for 72h and grinded to pass a 1 mm
  screen

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Material and Methods

• FDN content and FDN digestibility as in Goering
  VanSoest (1970).
• Only fermentative phase for 30 h of incubation

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Material and Methods

• Statistical Analysis
• Randomized block design.
• Model
• Y ? ?i ?j ?k ?i?j ?k?j ?i?k
  eijk
• Where ?icultivar ?jblock ?kage
• ?j, ?i?j and ?k?j were random
• MIXED procedure of SAS

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Results
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NDF digestibility of leaf- and stem-fractions
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Effect of cultivar on NDF digestibility of the
leaf-fraction
There was no genetic difference in leaf-NDFD
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Effect of cultivar on NDF digestibility of the
leaf-fraction
There was no genetic difference in the slope of
the decline of leaf-NDFD with age
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Effect of cultivar on NDF digestibility of the
stem-fraction
There was large genetic difference in stem-NDFD
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Effect of cultivar on NDF digestibility of the
stem-fraction
There was large genetic difference in the slope
of the decline of stem-NDFD with age
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Effect of cultivar on the slope of NDFD decline
with maturity
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Effect of cultivar on the slope of NDFD decline
with maturity
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Identification of genes
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PCR amplification was successful for all 7 genes
Lane 3 PAL, Lane 4 CAD, Lane 5 COMT, Lane 6
CCR, Lane 7 C4H, Lane 8 4CL.
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Similarity was high among grasses
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Conclusions

• There was significant genetic diversity for
  stem-NDFD, and no variation for leaf-NDFD.
• There was significant genetic diversity for the
  decline in NDFD with advancing maturity only for
  the stem fraction.

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Implications

• The slope of stem-NDFD or stem-NDFD with 90 days
  of regrowth could be used as a quality parameter
  for P. maximum selection or breeding programs, or
  for genetic manipulation programs.
• The continuing of this project will try to
  identify the genes controlling the decline of
  NDFD with advanced maturity

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