You’re Purple So Maybe You Can Brighten My Day

 A little background to start today. 

Plants contain a Pi-starvation-inducible (PSI) gene expression and complex morphological, physiological, and biochemical adaptations to low phosphorus. Plants have shown to up-regulate intracellular and secreted acid phosphatases in order to catalyze the hydrolysis of Pi from various phosphate monoesters when in an acidic environment. Purple acid phosphatases (PAPs) are a specific acid phosphatase class characterized by a bimetallic active site that causes a purple color. 29 PAP genes have been identified in Arabidopsis. Both transcriptional and posttranscriptional factors have been implicated in the control of  these PAPs. 

Ok, so maybe I am a bit biased in this post because I work on the above PAPs. To make this post even less credible, the paper I want to discuss is written by a PhD student I know. However, the recent work that has been conducted on PAPs provides some very helpful information about how plants respond to phosphorus deficiency that cannot be ignored simply due to some predispositions. 

 Hue and several researchers in my lab recently published a paper about one specific PAP and its role in phosphate response. AtPAP26 plays an important Pi-scavenging role in Arabidopsis during Pi stress. The details of this enzyme are examined in this paper. 

To start this study, the researchers decided to make a knockout mutant of Arabidopsis for this AtPAP26 gene. They used T-DNA insertions to make this knockout and then PCR analysis to confirm there were no transcripts present. This is evident in the figure below. To verify even further the success of the knockout, they used immunoblotting on the tissue and secreted media to check for any traces of AtPAP26 in the mutant. They of course did not find any traces of this enzyme.  

The atpap26 mutant exhibited 9- and 5-fold lower shoot and root APase activities respectively relative to the wildtype plant. This paper even goes on to talk about similar results that were obtained by Tomscha and coworkers when an acid phosphatase was knocked out (2004). 

The atpap26 mutant shoot development decreased by 30% in fresh weight relative to wildtype when grown in low phosphorus conditions in magenta boxes. It seems this mutant was not able to survive and grow as well without this AtPAP 26 enzyme. See graphs to right.  

To ensure that what was being observed could actually translate to crop conditions; they grew the mutant and wildtype in soil. The atpap26 mutant exhibited markedly impaired development during cultivation when in low phosphorus conditions. This can be seen in the very clear picture on the bottom left.

This study rightfully concludes that AtPAP26 encodes the principal vacuolar and major secreted APase isozyme up-regulated during time of low phosphorus. Other studies have shown that overexpression of secreted PAPs can improve plant biomass and phosphorus acquisition. If knocking out PAP26 decreases the ability of a plant to survive or grow in low phosphorus, then maybe overexpressing this PAP will help plants survive and acquire more phosphorus. This coincidentally is what I am currently working on.

We believe that AtPAP26 is a promising candidate for biotechnological strategies aimed at improving crop phosphorus acquisition.

Although I think this paper is written extremely well, and it covers a large amount of complex biochemical information, I can still be a little critical. 

I would have liked to see the method section before the results and discussion. It would allow the readers to know how the researchers actually performed the study before they found out what happened in the study.  Second, although I understood the paper and most readers of a plant physiology journal would have the cognitive abilities to decipher this article, I can’t help but wonder if this paper could have been written for a wider audience. This would allow the true significance of these types of papers reach a wider audience. And I think the more people know about this type of research, integration and open-communication between different scientific fields can more easily occur. 

Who knows, maybe my opinion is a “little” biased in this case. But good science is good science…

Reference

Tran H, Park J, Snedden W, Mullen M and Plaxton, W. 2010. The Dual-targeted Purple Acid Phosphatase Isozyme ATPAP26 is Essential for Efficient Acclimation of Arabidopsis to Nutritional Phosphate Deprivation. Plant Physio, 153, 1112-1122.