Characterization of the rice NLA family reveals a key role for OsNLA1 in phosphate homeostasis
Yang et al. Rice
Characterization of the rice NLA family reveals a key role for OsNLA1 in phosphate homeostasis
Jian Yang 0
Lan Wang 0 2
Chuanzao Mao 1
Honghui Lin 0
0 Ministry of Education Key Laboratory for Bio-Resource and Eco-Environment, College of Life Science, Sichuan University , Chengdu 610064 , China
1 State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University , Hangzhou 310058 , China
2 Biogas Institute of Ministry of Agriculture , Chengdu 610041 , China
Background: Phosphate (Pi), an essential mineral nutrient for plant development and reproduction, is one of the main components of fertilizers in modern agriculture. Previous research demonstrated that AtNLA1 mediates ubiquitination of Pi transporters in the plasma membrane and triggers their endocytosis and degradation in Arabidopsis. In this study, we researched the function of NLA homologous proteins in Pi homeostasis in rice. Findings: Two OsNLA homologs from rice (Oryza sativa L.) were identified by bioinformatics and phylogenetic analysis and designated OsNLA1 and OsNLA2. The OsNLA1 clustered with Arabidopsis AtNLA1, was expressed higher than OsNLA2 and was transcriptionally repressed under Pi-deficient condition. Loss-of-function of OsNLA1 caused P overaccumulation and growth inhibitions in both root and shoot under Pi-sufficient condition. Furthermore, mutation of OsNLA1 affected expression of Pi tranporters and root hair development under Pi-sufficient and/or Pi-deficient conditions. Conclusions: OsNLA1 plays a key role in maintaining phosphate homeostasis in rice.
Rice; Phosphate; OsNLA1; Pi-homeostasis
Findings
Phosphorus (P) is a mineral nutrient essential for plant
development and reproduction, and is integral to several
macromolecules such as phospholipids and nucleic acids.
Despite the indispensable role of P for plants, levels of
phosphate (orthophosphate; Pi), the only form of P that
can be taken up by plants, are commonly limited because
of chemical fixation and microbial activity
(Raghothama,
1999)
. To cope with suboptimal Pi conditions, plants have
developed a series of adaptive responses, such as
induction of Pi transporters and modification of root system
architecture
(Raghothama, 1999; Lin et al., 2009; Wu et
al., 2013)
. Plant uptake of Pi is largely mediated by plasma
membrane -localized Pi transporters belonging to the
PHOSPHATE TRANSPORTER1 (PT) symporter family.
Thirteen PT genes have been identified in rice (Oryza
sativa) and nine in Arabidopsis thaliana
(Goff et al., 2002;
Karthikeyan et al., 2002)
. OsPTs differ in tissue expression
patterns and affinities for Pi, resulting in diverse functions
in plants. For instance, the high-affinity Pi transporter
OsPT8 is universally expressed in rice, and is responsible
for half of its Pi uptake
(Chen et al., 2011; Jia et al., 2011)
.
Although most OsPTs in rice are induced at the
transcriptional level by Pi starvation or mycorrhizal symbiosis
(Yang et al., 2012; Secco et al., 2013)
, post-transcriptional
regulating of OsPT family proteins is also important to
their activities
(Gonzalez et al., 2005; Bayle et al., 2011;
Chen et al., 2011; Chen et al., 2015)
. NITROGEN
LIMITATION ADAPTATION (NLA), designated
AtNLA1 in this study, was first identified as a positive
regulator for the adaptability of Arabidopsis to nitrogen
limitation
(Peng et al., 2007)
, and later analysis of Pi
concentration revealed that the early senescence phenotype of
atnla mutant plants was due to Pi toxicity
(Kant et al.,
2011)
. In Arabidopsis, AtNLA1 can interact with AtPTs
members via its SPX domain, and mediate ubiquitination
of AtPTs in the plasma membrane and trigger their
endocytosis and degradation
(Lin et al., 2013; Park et al., 2014)
.
Recently, two research groups separately reported roles of
OsNLA1 in mantaining Pi homeostasis in rice
(Yue et al.,
2017; Zhong et al., 2017)
. Yue et al., (2017) additionally
reported OsNLA1 functioned as a ubiquitin ligase to
degrade Pi transporters in rice, with a similar function of
AtNLA1 in Arabidopsis.. In this study, we were interested
in the phylogenetic relationship of the NLA family and
expression of OsPTs and root hair development in osnla1
mutant.
An unrooted phylogenetic analysis of the NLA
family proteins with four monocots (B. distachyon, S.
bicolor, S. italica and rice) and five dicots (grapevine,
soybean, apple, M. truncatula and Arabidopsis),
revealed the presence of two distinct clades. Although
all plants had proteins belonging to clade I, in which
AtNLA1 involved in regulating Pi homeostasis was
present
(Kant et al., 2011)
, all monocots and only
some dicots had NLA members belonging to clade II
(Fig. 1a). This suggested that NLA members of clade
I conservatively functioned in maintaining Pi
homeostasis among different plant species. Quantitative
reverse-transcription PCR (qRT-PCR) was performed
on different tissues for rice plants grown in nutrient
solutions under Pi (...truncated)