c4 evolution Flashcards
C4 origin was when?
C4 probs first evolved 30mya
diversification of C4 when
5-7mya in late Meiocene in responce to reduction in CO2 atmos levels
C4 evolved how often ?
C$ evolved independently 66 times in >20 families
C4 is a complecation pathway it is unlikely to have evolved in one giant step, C3-C4 intermediates have been discovered these may?
- provide one of the stepping stones in the evolution of C4 from anestral C3 species
- be an evolutionary dead end
C3-C4 intermediates what are they? 3 tpes
C4-like types
c3/c4 types
hybrids
What was the first dicov C3-C4 inte?
Mollugo verticillata (1974)
CO2 compensation point is what in C3-C4 int?
light dependent
also changes with oxygen con –> PR still occurs
(not in C4)
C3-C4 have what anatomy?
most C4 like anatomy:
- intermediate not Kranz
- close association bt mt and chlorplasts
C3-4 int reduce photorespitation how?
not by removing the oxygenase reaction all together but ensuring the re-fixation of CO2 lost from PR
- therefore close association bt mt and chloroplasts
c3-4 int of Moricandia show differential expression of what?
allows for what to be recaptured?
is only expressed where? why?
Glycine decarboxylase
(2 glycine –> NH3 + Serine + CO2) in PR
70-90% recapture of respiratory CO2
Glycine decarboxylase only expressed in BSC, CO2 released in BSC can either be 1. fixed by rubisco in BSC or 2. escapes into MC
C3-C4 intermediates of ……… also exhibit C4 like biochemistry.
why?
have a high concentration of C4 pathway enzymes
…… species span developmental progress between c3 and c4, these species can be X or X
Cleome
C3 or C4
C4 evolution form C3 requires:
- increased veination
- larger BSC
- increase in number of chloroplast and mt in BS
- devision of PR metabolism between C3 and C4
- intervental distance bt MC and BSC decreases
Did novel C4 genes appear? What is likely to have happened
NO (genes already present in C3 plant)
genome duplication of preexisting genes - some changed to C4?
modification of regulatory sequences, C3 genes with C4 expression?
What is PEPC used for in C3 plants?
N assimilation
WHat changes are needed in PEPC genes to go from C3 to C4?
How are these changes thought to have arose?
- higher level of leaf-specific expression
- activity restricted to MC (not BSC)
- light inducibility
through changes in the promoter region of PEPC
….. contains what in its promoter region for PEPC?
Maize
novel cis acting element in PEPC promoter
Recent “….” for C4 genes in C3 plants as same ……. and similar ………. … to those in C$ plants. are we……..
conserved functional latency
same cis elements and promoter regions to those in C4 plants.
are we missing the transcription factor to turn it on?
How is differential expression of rubisco bt MC and BSC achieved?
repression loop in MC prevents the transciption of fully functioning small subunits in MC. loop activated by MC factors.
Trancription is enhanced in BSC due to presences of cis regulatory element with light inducible expression enhancer. Allow the transcription of rubisco in Bsc.
c4 ps was first reported?
40 years ago by Hatch and Slack
