Functional Characterization of Arabidopsis PHL4 in Plant Response to Phosphate Starvation

Abstract

Plants have evolved an array of adaptive responses to cope with phosphate (Pi) starvation. These responses are mainly controlled at the transcriptional level. In Arabidopsis, PHR1, a member of the MYB-CC transcription factor family, is a key component of the central regulatory system controlling plant transcriptional responses to Pi starvation. Its homologs in the MYB-CC family, PHL1 (PHR1-LIKE 1), PHL2, and perhaps also PHL3, act redundantly with PHR1 to regulate plant Pi starvation responses. The functions of PHR1’s closest homolog in this family, PHL4, however, have not been characterized due to the lack of its null mutant. In this work, we generated two phl4 null mutants using the CRISPR/Cas9 technique and investigated the functions of PHL4 in plant responses to Pi starvation. The results indicated that the major developmental, physiological, and molecular responses of the phl4 mutants to Pi starvation did not significantly differ from those of the wild type. By comparing the phenotypes of the phr1 single mutant and phr1phl1 and phr1phl4 double mutants, we found that PHL4 also acts redundantly with PHR1 to regulate plant Pi responses, but that its effects are weaker than those of PHL1. We also found that the overexpression of PHL4 suppresses plant development under both Pi-sufficient and -deficient conditions. Taken together, the results indicate that PHL4 has only a minor role in the regulation of plant responses to Pi starvation and is a negative regulator of plant development.

Two bifunctional inositol pyrophosphate kinases/phosphatases control plant phosphate homeostasis

“…Our work is in good agreement with the recent observation that mutations in the inositol polyphosphate biosynthesis pathway impact Pi signaling (Kuo et al, 2018). The fact that our quadruple mutant does not resemble wild-type plants may indicate that PP-InsPs regulate the activity of other components of the phosphate starvation response, such as additional transcription factors (Sun et al, 2015;Wang et al, 2018), phosphate transporters Wild et al, 2016), or other SPX-domain containing proteins (Park et al, 2014). The strong growth and developmental phenotypes of the vih1-2 vih2-4 double mutant may also hint at additional signaling functions for PP-InsPs unrelated to Pi homeostasis (Tan et al, 2007;Sheard et al, 2010;Mosblech et al, 2011;Laha et al, 2015Laha et al, , 2016Wild et al, 2016).…”

“…Shoot phosphate levels in the quadruple mutant are significantly higher when compared to either wildtype or phr1 phl1 double mutants ( Figure 4E). This suggests that VIH1 and VIH2 generated PP-InsPs regulate the activity not only of PHR1 and PHL1, but possibly of other Pi starvation responsive transcription factors such as PHL3 and/or PHL4 (Sun et al, 2015;Wang et al, 2018) or of other PP-InsP responsive Pi signaling components (Hamburger et al, 2002;Wild et al, 2016).…”

Long non-coding RNAs: emerging players regulating plant abiotic stress response and adaptation

“…Nutrient acquisition from soil remains one of the essential physiological processes for regulating plant growth and development [125]. Several molecular mechanisms, including many nutrient transporters, are actively involved in plant nutrient homeostasis [126,127]. Among the various non-coding regulatory RNAs, evidence of miRNAs and lncRNAs regulating nutrient acquisition has been found in various plants [11,14,61].…”

“…The availability of soil inorganic phosphate (Pi) to plants is constrained by several factors that limit overall plant growth and development [129]. Little information is available on the complex regulatory network of P homeostasis in plants [127,130]. Several molecular and biochemical mechanisms are activated by plants to improve soil inorganic phosphate availability and increase phosphorus use efficiency (PUE) [127,129,130].…”

“…Little information is available on the complex regulatory network of P homeostasis in plants [127,130]. Several molecular and biochemical mechanisms are activated by plants to improve soil inorganic phosphate availability and increase phosphorus use efficiency (PUE) [127,129,130]. In this context, the role of miRNAs controlling phosphate availability has been reported in various plants [110].…”