Abstract
Cold acclimation is an essential response in higher plants to survive freezing temperatures. Here, we report that two independent mutant alleles of the H-subunit of Mg-chelatase, CHLH, gun5-1 and cch in Arabidopsis are sensitive to low temperatures. Plants were grown in photoperiodic conditions and exposed to low temperatures for short- and long-term periods. Tetrapyrrole biosynthesis was initially significantly inhibited in response to low temperature but recovered in wild type (Col-0), although the tetrapyrrole levels were lower in cold compared to control conditions. The gun5-1 and cch alleles showed an inability to recover chlorophyll biosynthesis in addition to a significant decrease in freezing tolerance. We found that the impaired plastid function in the CHLH mutant plants resulted in compromised de novo protein synthesis at low temperatures. The expression of the transcription factors CBF1-3 was super-induced in gun5-1 and cch mutant alleles but expression levels of their target genes, COR15a, COR47 and COR78 were similar or even lower compared to Col-0. In addition, the protein levels of COR15a were lower in gun5-1 and cch and a general defect in protein synthesis could be seen in the gun5-1 mutant following a 35S labelling experiment performed at low temperature. Taken together, our results demonstrate the importance of a functional chloroplast for the cold acclimation process and further suggest that impaired plastid function could result in inhibition of protein synthesis at low temperature.
Highlights
Changes in ambient temperatures affect growth and survival of most living organisms
The chlorophyll levels in response to low temperature confirm the visible phenotype for both genotypes, wild type showed an increase in total chlorophyll and the chlorophyll a/b ratio while the gun5 mutant displayed a sharp decrease in total chlorophyll content and an increased chlorophyll a/b ratio (Fig 2)
The CHLH mutants have clearly impaired ability to acclimate to low temperatures and as a consequence the mutants are more freezing sensitive compared to wild type
Summary
Changes in ambient temperatures affect growth and survival of most living organisms. To overcome any negative effect of exposure to low temperatures, many species have evolved an adaptive response named cold acclimation [1,2]. Cold acclimation enables an organism to survive freezing temperatures if they first are exposed to low non-freezing temperatures for a period of time. Cold acclimation is very complex and comprises a multitude of changes to the metabolism of the plant [2]. A massive change in gene transcription is an PLOS ONE | DOI:10.1371/journal.pone.0138010. A massive change in gene transcription is an PLOS ONE | DOI:10.1371/journal.pone.0138010 September 14, 2015
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