the Lotus symbiotic sulfate transporter (sst1)
mutant coding for that predicted sulfate trans-
porter was identified to be crucial for nitrogen
fixation (Wienkoop and Saalbach 2003 ; Krusell
et al. 2005 ).sst1plants form ineffective nodules
and cannotfix nitrogen efficiently, whereas the
mutant grows normally under non-symbiotic
conditions (Krusell et al. 2005 ). Thus, the pro-
teomics data lead to the hypothesis that the plant
sulfate transporter is localized on the symbiosome
membrane and essential for transporting sulfate
from plant cytoplasma to the rhizobia (Krusell
et al. 2005 ).
Currently, most focus on comparative root
proteomics has been on stress condition such as
high salt,flooding, and temperature to identify
regulated proteins in the defense pathways
(Nanjo et al. 2012 ; Salavati et al. 2012 ; Dumont
et al. 2011 ; Ahsan et al. 2010 ; Rodriguez-Celma
et al. 2011 ), whereas approaches focusing on the
symbiotic initiation of infection and organogen-
esis in the root infection zone are less developed.
However, with the more sensitive proteomics
methods, this can be used to elucidate novel
knowledge at the protein level for initiating the
infection and organogenesis pathways.
18.5 Proteomics of Post
Translational Modifications in
Lotus
The majority of proteins/enzymes have at least
one PTM that can be essential for protein func-
tion, activity, stability, or degradation. One of the
most common PTMs is N-glycosylation for
which the functionality can be dependent or even
independent of the protein carrier (Sumer-Bay-
raktar et al. 2011 ; Anthony and Ravetch 2010 ;
Ohtsubo and Marth 2006 ). InLotus, a glycomics
study of the mature seed globulin fraction dis-
played a total of 19 differentN-glycan structures
including high mannosidic, pauci-mannosidic,
and complex structures (Dam et al. 2013 ). The
glycoproteomics data indicates that the high
mannosidic structures are mainly linked toLotus
convicilin protein 2 (LCP2), pauci-mannosidic
structures to a predicted lectin, and complex
structures to a predicted peptidase (Dam et al.
2013 and unpublished data).
Protein phosphorylation/dephosphorylation is
a common activation/deactivation mechanism for
signaling cascades such as initiation of nodule
formation together with a prompt response to
pathogens. Thus, within the last decade, several
plant phosphoproteomics studies were performed
(Nakagami et al. 2010 ; Yang et al.2013a, b;
Wang et al. 2013 ). Proteomics and phosphopro-
teomics datasets ofLotusnodules, spontaneous
nodules, and roots from wild-type andsponta-
neous nodule formation 1(snf1) plants have been
generated and is currently being analyzed for
proteins and phosphorylations needed for the
infection and organogenesis pathways (unpub-
lished data). Furthermore, inLotusseedlings, 721
and 931 phosphopeptides were identified from
the cotyledon and hypocotyl, respectively, with
an overrepresentation of the GO term “RNA
processing”in the hypocotyl (Ino et al. 2013 ).18.6 PerspectivesInLotus, proteome reference maps are available
for seeds, pods, nodules, and roots together with
relative quantification between developmental
stages of all tissues analyzed. With use of the
LORE1 resource (Urbanski et al. 2012 ; Fukai
et al. 2012 ), containing thousands of mutant
lines, comparative proteomics of wild type and
different mutants of interest is now possible. This
combined with the large number of transcripto-
mics data available forLotuscan reveal essential
proteins for nodulation, infection, and the high
protein level in the seed. At the PTM level,
glycomics and glycoproteomics from LORE1
seeds which have a LORE1 insert in enzymes
catalyze theN-glycan maturation has been initi-
ated. In conclusion, all types of comparative
proteomics analysis between wild-type and
LORE1 mutants can be performed to identify
difference at the proteome and/or PTM levels to
increase the particular knowledge in areas of
interest.18 Proteomics 205