The secretion of the bacterial phytase PHY‐US417 by Arabidopsis roots reveals its potential for increasing phosphate acquisition and biomass production during co‐growth

Abstract

SummaryPhytic acid (PA) is a major source of inorganic phosphate (Pi) in the soil; however, the plant lacks the capacity to utilize it for Pi nutrition and growth. Microbial phytases constitute a group of enzymes that are able to remobilize Pi from PA. Thus, the use of these phytases to increase the capacity of higher plants to remobilize Pi from PA is of agronomical interest. In the current study, we generate transgenic Arabidopsis lines (ePHY) overexpressing an extracellular form of the phytase PHY‐US417 of Bacillus subtilis, which are characterized by high levels of secreted phytase activity. In the presence of PA as sole source of Pi, while the wild‐type plants show hallmark of Pi deficiency phenotypes, including the induction of the expression of Pi starvation‐induced genes (PSI, e.g. PHT1;4) and the inhibition of growth capacity, the ePHY overexpressing lines show a higher biomass production and no PSI induction. Interestingly, when co‐cultured with ePHY overexpressors, wild‐type Arabidopsis plants (or tobacco) show repression of the PSI genes, improvement of Pi content and increases in biomass production. In line with these results, mutants in the high‐affinity Pi transporters, namely pht1;1 and pht1;1‐1;4, both fail to accumulate Pi and to grow when co‐cultured with ePHY overexpressors. Taken together, these data demonstrate the potential of secreted phytases in improving the Pi content and enhancing growth of not only the transgenic lines but also the neighbouring plants.

Heterologous Expression of Secreted Bacterial BPP and HAP Phytases in Plants Stimulates Arabidopsis thaliana Growth on Phytate

“…Similarly, expression of B. subtilis 168phyA phytase in A. thaliana led to a higher shoot dry weight and an increase in phosphorus content by 100% compared to the wild type ( Lung et al, 2005 ). Similar results have more recently been obtained with a related BPP phytase PHY-US417 expressed in A. thaliana ( Belgaroui et al, 2014 , 2016 ).…”

“…Most of such phytases used in transgenic research are members of the HAP type of phytases ( Pen et al, 1993 ; Verwoerd et al, 1995 ; Brinch-Pedersen et al, 2000 ; Ponstein et al, 2002 ; Hong et al, 2004 ; Bilyeu et al, 2008 ; Wang et al, 2013 ). In addition, a few studies reported successful use of BPP phytases ( Yip et al, 2003 ; Lung et al, 2005 ; Chan et al, 2006 ; Belgaroui et al, 2014 ; Belgaroui et al, 2016 ) and PAP enzymes ( Xiao et al, 2005 ; Ma et al, 2009 , 2012 ). TTP phytases, which represent a relatively rare family of phytases found mostly in ruminant bacteria ( Yanke et al, 1998 ), have also been utilized ( Hong et al, 2004 ).…”

“…168phyA phytase has previously been expressed in tobacco and A. thaliana , though under different promoters ( Yip et al, 2003 ; Lung et al, 2005 ; Chan et al, 2006 ). A closely related phytase from B. subtilis strain 417 (72% amino acid identity and 84% similarity to 168phyA phytase) has also recently been used for this purpose ( Belgaroui et al, 2014 , 2016 ). When grown on phytate, plants expressing these BPP-type phytases displayed twofold higher biomass levels ( Belgaroui et al, 2016 ), as well as a significant increase in shoot P concentration compared to control plants ( Lung et al, 2005 ; Belgaroui et al, 2016 ).…”

“…A closely related phytase from B. subtilis strain 417 (72% amino acid identity and 84% similarity to 168phyA phytase) has also recently been used for this purpose ( Belgaroui et al, 2014 , 2016 ). When grown on phytate, plants expressing these BPP-type phytases displayed twofold higher biomass levels ( Belgaroui et al, 2016 ), as well as a significant increase in shoot P concentration compared to control plants ( Lung et al, 2005 ; Belgaroui et al, 2016 ). However, in some cases these phenotypes were accompanied by negative effects on plant physiology, including smaller size and lower germination rates of transgenic tobacco seeds expressing 168phyA phytase ( Yip et al, 2003 ; Lung et al, 2005 ).…”

Characterization of the Catalytic Structure of Plant Phytase, Protein Tyrosine Phosphatase-Like Phytase, and Histidine Acid Phytases and Their Biotechnological Applications

“…Plant growth and productivity can be hindered by low availability of phosphorus (P) in the soil [ 14 ]. Therefore, plants have developed mechanisms to improve soil phosphorus availability, with emphasis on the participation of purple acid phosphatases (PAPs).…”