Technology at its best!

How about we just concentrate on plants we KNOW can thrive in low phosphorus conditions for today.

White lupine (Lupinus albus) is a very P-deficient tolerant plant species and thus it can be used for studying its adaptations to low phosphorus. 

When under phosphorus stress, white lupin has been shown to develop many lateral roots that contain several clusters. These clusters are subsequently covered with root hairs. These adaptations all serve to increase the surface area of the roots to allow the crops to absorb more phosphorus. These roots can also release organic acids, as I have previously discussed, to help mobilize the phosphate from its insoluble form. 

 

 Several genes have been identified in response to low phosphorus in white lupin and microarrays have additionally helped identify the expression of these genes. Recently, researchers have started to use microRNAs (miRNAs). These are endogenous single-stranded noncoding RNAs. They are known to negatively regulate post-transcription of genes through interactions with coding regions of their targets. In plants, miRNAs regulate the expression of a large number of genes that control growth. Additionally, several members of miRNA have been shown to regulate stress response and nutrient compensation.

Currently, the knowledge of miRNA regulation of phosphate nutrition at a genomic level is limited. Therefore, this past summer (2010) several researchers at the Agricultural University in China set out to analyze how miRNA is regulated in white lupin during phosphorus stress.

The above information is all covered in the introduction of this paper. In my opinion, there was simply not enough information to prepare the reader for the experiments to come. Luckily, I have some background knowledge in these microarrays, or I would have been totally lost and turned the page to the next article in the journal.

The authors continue from the introduction to the method section. They describe in detail how they went about this study. After the plants were cultivated under either phosphorus stress or no phosphorus stress, the total RNAs were extracted from the tissues. From there, the RNAs were hybridized to an array containing hundreds of conserved plant miRNA sequences. 

 Only changes in miRNA abundance greater that 2 were accepted. The researchers found that 35 miRNA families representing 167 miRNAs were significantly probed during phosphorus stress (please see the table above). The results also show that roots, leaves and stems activate a distinct set of miRNA genes when under low phosphorus. However, some overlapping miRNAs were detected in all the tissues. This data can be seen in the figure to the left. This figure is such an unbelievable simply and effective way to show these results! I am impressed.

 In order to validate their findings, the researchers also chose to run the very reliable RT-PCR on all the tissues. This experiment did in fact confirm their findings (shown below).

To conclude their paper, the researchers go into a very comprehensive discussion. They concluded that the differential expression of phosphate responsive miRNA genes should be seen as a morphological adaptation and regulatory response to low phosphorus. The results also imply that the miRNAs participate in long-distance communication.

The majority of the discussion is spent on one miRNA that was found in these plants. It has been shown in other studies that miR399 is responsible for homeostasis control in Arabidopsis.  The current results show the up-regulation expression of miR399 in leaves of white lupin, suggesting that miR399 may also play a role in phosphorus remobilization in aerial parts. However, there was no miR399 in the roots. The authors suggest that this is possible because legume plants may have a different mechanism for phosphorus acquisition than Arabidopsis. 

My favorite part of this paper comes near the end where they discuss using a computational approach to search for the potential target genes. Four target miRNA were predicted to code ATP sulfurylases and another was thought to a ribosomal protein. Now that just proves how cool biotechnology can be!

“Taken together,

we have identified a set of miRNAs in white lupin under phosphate

deficiency and observed that some of the miRNAs differentially

expressed. This is the first thorough miRNA expression study done

in a fabaceae species adopted to grow under the low P deficiency.

This study would help our understanding of the network and

interactive processes of small RNAs in regulating plant adaptive

response to P deficiency.”

I mean the above quote sums up everything I could say and more about this paper. Although it gets off to a bit of shaky start and it is an extremely difficult paper to follow, the results are quite impressive.

Imagine if crops could eventually express these miRNAs involved in phosphate stress, the world would be a fatter place…

Reference

Zhu, Y. Zeng, H. Dong, C. Ming Yin, X. Shen, Q. 2010. microRNA expression profiles associated with phosphorus deficiency in white lupin (Lupinus albus L.). Plant Science, 178, 23–29.