An ethylene-induced NAC transcription factor acts as a multiple abiotic stress responsor in conifer

The proper response to various abiotic stresses is essential for plants’survival to overcome their sessile nature,especially for perennial trees with very long-life cycles.However,in conifers,the molecular mechanisms that coordinate multiple abiotic stress responses remain elusive.Here,the transcriptome response to various abiotic stresses like salt,cold,drought,heat shock and osmotic were systematically detected in Pinus tabuliformis(P.tabuliformis)seedlings.We found that four transcription factors were commonly induced by all tested stress treatments,while PtNAC3 and PtZFP30 were highly up-regulated and co-expressed.Unexpectedly,the exogenous hormone treatment assays and the content of the endogenous hormone indicates that the upregulation of PtNAC3 and PtZFP30 are mediated by ethylene.Time-course assay showed that the treatment by ethylene immediate precursor,1-aminocyclopropane-1-carboxylic acid(ACC),activated the expression of PtNAC3 and PtZFP30 within 8 hours.We further confirm that the PtNAC3 can directly bind to the PtZFP30 promoter region and form a cascade.Overexpression of PtNAC3 enhanced unified abiotic stress tolerance without growth penalty in transgenic Arabidopsis and promoted reproductive success under abiotic stress by shortening the lifespan,suggesting it has great potential as a biological tool applied to plant breeding for abiotic stress tolerance.This study provides novel insights into the hub nodes of the abiotic stresses response network as well as the environmental adaptation mechanism in conifers,and provides a potential biofortification tool to enhance plant unified abiotic stress tolerance.

Phosphorus lights up the trade-off between growth and immunity

How plants respond simultaneously to various biotic and abiotic stresses to balance growth and immunity is an old but vibrant topic.Plants need to effectively integrate multiple signaling inputs to make the final decision and,thus,use limited resources efficiently.Typically,plant secondary metabolites,including phytohormones,are the key to modulate investment of resources into immunity or growth.However,the molecular mechanisms underlying this allocation dilemma are far from being understood.

NIGT1 represses plant growth and mitigates phosphate starvation signaling to balance the growth response tradeoff in rice

Inorganic phosphate(Pi)availability is an important factor which affects the growth and yield of crops,thus an appropriate and effective response to Pi fluctuation is critical.However,how crops orchestrate Pi signaling and growth under Pi starvation conditions to optimize the growth defense tradeoff remains unclear.Here we show that a Pi starvationinduced transcription factor NIGT1(NITRATE-INDUCIBLE GARP-TYPE TRANSCRIPTIONAL REPRESSOR 1)controls plant growth and prevents a hyper-response to Pi starvation by directly repressing the expression of growth-related and Pisignaling genes to achieve a balance between growth and response under a varying Pi environment.NIGT1 directly binds to the promoters of Pi starvation signaling marker genes,like IPS1,mi R827,and SPX2,under Pi-deficient conditions to mitigate the Pi-starvation responsive(PSR).It also directly represses the expression of vacuolar Pi efflux transporter genes VPE1/2 to regulate plant Pi homeostasis.We further demonstrate that NIGT1 constrains shoot growth by repressing the expression of growth-related regulatory genes,including brassinolide signal transduction master regulator BZR1,cell division regulator CYCB1;1,and DNA replication regulator PSF3.Our findings reveal the function of NIGT1 in orchestrating plant growth and Pi starvation signaling,and also provide evidence that NIGT1 acts as a safeguard to avoid hyper-response during Pi starvation stress in rice.

Two RING-Finger Ubiquitin E3 Ligases Regulate the Degradation of SPX4, An Internal Phosphate Sensor, for Phosphate Homeostasis and Signaling in Rice

SPX-domain-containing proteins (SPXs) play an important role in inorganic phosphate (Pi) sensing,signaling,and transport in eukaryotes.In plants,SPXs are known to integrate cellular Pi status and negatively regulate the activity of Pi central regulators,the PHOSPATE STARVATION RESPONSE proteins (PHRs).The stability of SPXs,such as SPX4,is reduced under Pi-deficient conditions.However,the mechanisms by which SPXs are degraded remain unclear.In this study,using a yeast-twhybrid screen we iden.tified two RING-finger ubiquitin E3 ligases regulating SPX4 degradation,designated SDEL1 and SDEL2,which were post-transcriptionally induced by Pi starvation.We found that both SDELs were located in the nucleus and cytoplasm,had ubiquitin E3 ligase activity,and directly ubiquitinated the K^213 and K^299 lysine residues in SPX4 to regulate its stability.Furthermore,we found that PHR2,a Pi central regulator in rice,could compete with SDELs by interacting with SPX4 under Pi-sufficient conditions,which protected SPX4 from ubiquitination and degradation.Consistent with the biochemical function of SDEL1 and SDEL2,overexpression of SDEL1 or SDEL2 resulted in Pi overaccumulation and induced Pi-starvation signaling even under Pi-sufficient conditions.Conversely,their loss-of-function mutants displayed decreased Pi accumulation and reduced Pi-starvation signaling.Collectively,our study revealed that SDEL1 and SDEL2 facilitate the degradation of SPX4 to modulate PHR2 activity and regulate Pi homeostasis and Pi signaling in response to external Pi availability in rice.

A reciprocal inhibitory module for Pi and iron signaling

Phosphorous(P)and iron(Fe),two essential nutrients for plant growth and development,are highly abundant elements in the earth's crust but often display low availability to plants.Due to the ability to form insoluble complexes,the antagonistic interaction between P and Fe nutrition in plants has been noticed for decades.However,the underlying molecular mechanism modulating the signaling and homeostasis between them re-mains obscure.Here,we show that the possible iron sensors HRZs,the iron deficiency-induced E3 ligases,could interact with the central regulator of phosphate(Pi)signaling,PHR2,and prompt its ubiquitination at lysine residues K319 and K328,leading to its degradation in rice.Consistent with this,the hrzs mutants dis-played a high Pi accumulation phenotype.Furthermore,we found that iron deficiency could attenuate Pi star-vation signaling by inducing the expression of HRZs,which in turn trigger PHR2 protein degradation.Inter-estingly,on the other hand,rice PHRs could negatively regulate the expression of HRZs to modulate iron deficiency responses.Therefore,PHR2 and HRZs form a reciprocal inhibitory module to coordinate Pi and iron signaling and homeostasis in rice.Taken together,our results uncover a molecular link between Pi and iron master regulators,which fine-tunes plant adaptation to Pi and iron availability in rice.

Responses of ramie(Boehmeria nivea L.)to increasing rare earth element(REE)concentrations in a hydroponic system

A number of studies have focused on the effects of rare earth elements(REEs) on crop plants,while little attention has been paid on how tolerant plant species respond to increasing mixed REE concentrations.In this study,ramie(Boehmeria nivea L.) was exposed to a series of REE concentrations prepared with equimolar mixtures of 16 REEs(i.e.0,1.6,8,16,80,160,400,800 μmol/L) in order to explore REE accumulation and fractionation characteristics in ramie and the responses of this plant to mixed REEs.Results show that ramie root and shoot biomasses are unaffected under lower REE concentrations(1.6-80 μmol/L),while the growth of ramie and the uptake of nutrients especially Ca and Mn are largely inhibited under higher REE concentrations(160-800 μmol/L).The P and Mo concentrations in the roots increase with the increasing REE concentrations in the solution,suggestive of an involvement of P and Mo in dealing with the high concentrations of REEs in this plant.The preferential uptake of Ce and heavy REEs(HREEs) and the preferential transport of HREEs within the plant lead to a positive Ce anomaly and a HREE enrichment in ramie leaves.Our study suggests that ramie could be a good candidate for the phyto re mediation of heavily REE-contaminated soils(e.g.,REE mine tailings in southern China).Our results also shed light on points of taking into account phytoremediation management strategies of REEcontaminated soils(e.g.,P and Mo fertilization).