Proline Accumulation Is Regulated by Transcription Factors Associated with Phosphate Starvation

Abstract

ORCID ID: 0000-0002-9163-9875 (L.S.).Pro accumulation in plants is a well-documented physiological response to osmotic stress caused by drought or salinity. In Arabidopsis (Arabidopsis thaliana), the stress and ABA-induced D1-PYRROLINE-5-CARBOXYLATE SYNTHETASE1 (P5CS1) gene was previously shown to control Pro biosynthesis in such adverse conditions. To identify regulatory factors that control the transcription of P5CS1, Y1H screens were performed with a genomic fragment of P5CS1, containing 1.2-kB promoter and 0.8-kb transcribed regions. The myeloblastosis (MYB)-type transcription factors PHOSPHATE STARVATION RESPONSE1 (PHR1) and PHR1-LIKE1 (PHL1) were identified to bind to P5CS1 regulatory sequences in the first intron, which carries a conserved PHR1-binding site (P1BS) motif. Binding of PHR1 and PHL1 factors to P1BS was confirmed by Y1H, electrophoretic mobility assay and chromatin immunoprecipitation. Phosphate starvation led to gradual increase in Pro content in wild-type Arabidopsis plants as well as transcriptional activation of P5CS1 and PRO DEHYDROGENASE2 genes. Induction of P5CS1 transcription and Pro accumulation during phosphate deficiency was considerably reduced by phr1 and phl1 mutations and was impaired in the ABA-deficient aba2-3 and ABA-insensitive abi4-1 mutants. Growth and viability of phr1phl1 double mutant was significantly reduced in phosphate-depleted medium, while growth was only marginally affected in the aba2-3 mutants, suggesting that ABA is implicated in growth retardation in such nutritional stress. Our results reveal a previously unknown link between Pro metabolism and phosphate nutrition and show that Pro biosynthesis is target of cross talk between ABA signaling and regulation of phosphate homeostasis through PHR1-and PHL1-mediated transcriptional activation of the P5CS1 gene.

Light Control of Salt-Induced Proline Accumulation Is Mediated by ELONGATED HYPOCOTYL 5 in Arabidopsis

“…Only HY5 binding sites are indicated in the schematic maps. HMT corresponds to histone merthyltransferase and TF indicates other transcription factors which can regulate transcription of P5CS1 (Feng et al, 2016;Aleksza et al, 2017;Fu et al, 2018) or PDH1 (Satoh et al, 2004;Weltmeier et al, 2006;Dietrich et al, 2011). Lightcontrolled HY5 binds to the promoters of both genes and contributes to P5CS1 activation, but has only a minor effect on PDH1 expression.…”

“…Proline accumulates to high levels in plants at low water potential caused by drought, salinity and in response to several other abiotic and biotic stresses (Kemble and Macpherson, 1954;Schat et al, 1997;Fabro et al, 2004;Yang et al, 2009;Szabados and Savoure, 2010;Aleksza et al, 2017). Proline was suggested to act as osmoprotectant stabilizing enzymes or maintaining redox equilibrium in adverse conditions (Delauney and Verma, 1993;Székely et al, 2008;Szabados and Savoure, 2010;Verslues and Sharma, 2010;Kavi Kishor and Sreenivasulu, 2014;Per et al, 2017).…”

“…PDH1 (AT3G30775) is repressed in high osmotic conditions and is induced by proline during stress recovery (Kiyosue et al, 1996). Compared to PDH1, PDH2 has a very low expression level, which is however induced during phosphate starvation (Aleksza et al, 2017). ABA, reactive oxygen species, calcium, and lipid signals were implicated in the regulation of proline metabolism (Thiery et al, 2004;Parre et al, 2007;Ben Rejeb et al, 2015).…”

“…A number of cis regulatory sequences have been identified in promoters or 5′UTRs of key metabolic genes, but direct evidence on promoter-binding transcription factors and their function is scarce (Fichman et al, 2015;Zarattini and Forlani, 2017). We have recently described that PHOSPHATE STARVATION RESPONSE 1 (PHR1) and PHOSPHATE STARVATION RESPONSE LIKE-1 (PHL1) transcription factors bind the P1BS motif in the first intron of P5CS1, upregulate its expression, and promote proline accumulation during phosphate starvation (Aleksza et al, 2017). A recent report showed that the transcription factor ANAC55 (Arabidopsis NAM, ATAF, and CUC) is a positive regulator of P5CS1 expression and proline accumulation in high osmotic conditions, although direct binding to P5CS1 promoter elements was not demonstrated (Fu et al, 2018).…”

Phosphate and phosphite differentially impact the proteome and phosphoproteome of Arabidopsis suspension cell cultures

“…CDPK3, 6 and 19 are all involved in ABA signaling(Zou et al, 2015;Li et al, 2018), which itself has a 401 role in Pi-nutrition. Aleksza and colleagues (2017) determined that ABA can stimulate proline production 402during Pi-starvation through myeloblastosis (MYB) and ABA-responsive element binding protein 403 (AREB) transcription factor mediated increases in D1-PYRROLINE-5-CARBOXYLATE 404 SYNTHETASE 1 (P5CS1) expression levels(Aleksza et al, 2017). Here, we find ABA-RESPONSIVE…”