The Lotus japonicus Genome

depend on its assimilation by nitrate reductase,
and hence, it is unlikely to be due to a nutritional
effect (Carroll and Mathews 1990 ). Two clear-cut
early phenotypes consisting of the inhibition of
cortical cell division and down-regulation of the
NIN gene expression were reported in Lotus
japonicuswild-type plants inoculated withM.
lotiin the presence of high KNO 3 concentrations
(Barbulova et al. 2007 ). However, the mecha-
nisms and factors involved in the signaling
pathways leading to the nitrate-dependent nodule
organogenesis inhibition are still largely
unknown. A possible role played by nitrate in the
control of auxin, ethylene, and/orflavonoid sig-
naling pathways has been postulated (Cho and
Harper 1991 ; Caba et al. 2000 ). Recently, a role
for nitrate-responsive CLE peptides as the main
actors in the transduction of the root signal to the
Leucine-rich Repeat Receptor Kinases (HAR1/
NARK1/NST1/SUNN)-dependent mechanism
governing autoregulation of nodule numbers has
been reported in L. japonicus, Soybean, and
Medicago truncatula and even in these cases
both local and/or systemic mechanisms of con-
trol were proposed (Okamoto et al. 2009 ; Mortier
et al. 2010 ; Reid et al. 2011 ).

12.3 Lotus JaponicusNPF and NRT2

Families: Genomic

Organization and Expression

Profiles

The retrieval of NPF sequences from the L.

japonicus whole-genome sequence resource

(Sato et al. 2008 ;http://www.kazusa.or.jp/lotus/)

leading to the identification of 37 putative mem-

bers has been recently published (Criscuolo et al.

2012 ). Sequence analyses predicted the con-

served structural arrangement of 12 transmem-

brane domains connected by short peptide loops

for almost the totality of theL. japonicusNPF

members (Table12.2). A further search led to the

identification of two additional complete NPF

sequences and 32 un-completed unique sequen-

ces of predictedNPFgenes, indicating a size of

around 70 members for theL. japonicusfamily.

Fifty-one genes are physically mapped on the

Lotus genome indicating a distribution on all the

six chromosomes. Most are found on chromo-

somes 1, 2, and 4 with sixteen,fifteen, andfifteen

genes, respectively, whereas one gene is located

on chromosome 3 and two on chromosomes 5

Table 12.1 (continued)
Clade L. japonicus
Locus id.

New

name

A. thaliana/old name M. truncatula/

old name

O. sativa,

A.

glutinosa,

B. napus

chr4.

CM0026.860

LjNPF8.4 AtNPF8.4/AtPTR4

chr4.

CM0026.870

LjNPF8.5 AtNPF8.5/AtPTR6

chr2.

LjT15I01.230

LjNPF8.6

chr4.

CM0026.880

LjNPF8.7

OsNPF8.9
(nitrate)
TheA. thalianaandM. truncatulaNPF members are also included for comparison, as well as the functionally
characterizedO. sativaNPF7.3 and NPF8.9 (Lin et al. 2000 ),Brassica napusNRT1.2 (Zhou et al. 1998 ), andAlnus
glutinosaDCAT1 (Jeong et al. 2004 ) members. Clade numbers indicate the different subfamilies. When known, the
transported substrates are indicated in brackets. In bold are theL. japonicusNPF members with a nodule-induced profile
of expression. At;Arabidopsis thaliana.MtMedicago truncatula.OsOriza sativa.BnBrassica napus.AgAlnus
glutinosa

130 V.T. Valkov and M. Chiurazzi