Dynamic proline metabolism: importance and regulation in water limited environments.

Govinal B Bhaskara,Paul E Verslues,Tsu-Hao Yang

doi:10.3389/fpls.2015.00484

Govinal B Bhaskara, Paul E Verslues + Show 1 more

Open Access

https://doi.org/10.3389/fpls.2015.00484

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Abstract

Drought-induced proline accumulation observed in many plant species has led to the hypothesis that further increases in proline accumulation would promote drought tolerance. Here we discuss both previous and new data showing that proline metabolism and turnover, rather than just proline accumulation, functions to maintain growth during water limitation. Mutants of Δ1-Pyrroline-5-Carboxylate Synthetase1 (P5CS1) and Proline Dehydrogenase1 (PDH1), key enzymes in proline synthesis and catabolism respectively, both have similar reductions in growth during controlled soil drying. Such results are consistent with patterns of natural variation in proline accumulation and with evidence that turnover of proline can act to buffer cellular redox status during drought. Proline synthesis and catabolism are regulated by multiple cellular mechanisms, of which we know only a few. An example of this is immunoblot detection of P5CS1 and PDH1 showing that the Highly ABA-induced (HAI) protein phosphatase 2Cs (PP2Cs) have different effects on P5CS1 and PDH1 protein levels despite having similar increases in proline accumulation. Immunoblot data also indicate that both P5CS1 and PDH1 are subjected to unknown post-translational modifications.

Highlights

Pyrroline-5-Carboxylate Synthetase1 (P5CS1) (AT2G39800) and Proline Dehydrogenase1 (PDH1) (AT3G30775) gene expression patterns suggest that proline synthesis is high and proline catabolism suppressed in photosynthetic tissue during stress
P5CS1 and PDH1 expression, along with other observations made it clear that proline metabolism is highly regulated and proline accumulation during drought is not a symptom of stress injury nor a result of passive accumulation caused by growth reduction
This view is based on the transcriptional up-regulation of P5CS1 and decreased expression of PDH1 during drought stress as well as hypotheses that proline turnover under stress is low and that proline accumulation is cell autonomous and isolated from other metabolic pathways (Verslues and Sharma, 2010). It implies that transcriptional regulation of P5CS1 and PDH1 are main determinants of proline accumulation. We propose that these ideas need to be critically examined and present some evidence that support a more dynamic view of proline metabolism during drought and suggest the existence of multiple layers of regulation

Summary

Introduction

Mutants of ∆1-Pyrroline-5-Carboxylate Synthetase1 (P5CS1) and Proline Dehydrogenase1 (PDH1), key enzymes in proline synthesis and catabolism respectively, both have similar reductions in growth during controlled soil drying. Rather than other metabolites, accumulates to high levels as well as how proline metabolism may be modified to improve drought tolerance are long standing questions in plant stress biology (Lehmann et al, 2010; Szabados and Savouré, 2010; Verslues and Sharma, 2010; Kavi Kishor and Sreenivasulu, 2014).

Results

Conclusion