Polyamine metabolic canalization in response to drought stress in Arabidopsis and the resurrection plant Craterostigma plantagineum

Abstract

In this work, we have studied the transcriptional profiles of polyamine biosynthetic genes and analyzed polyamine metabolic fluxes during a gradual drought acclimation response in Arabidopsis thaliana and the resurrection plant Craterostigma plantagineum. The analysis of free putrescine, spermidine and spermine titers in Arabidopsis arginine decarboxylase (adc1-3, adc2-3), spermidine synthase (spds1-2, spds2-3) and spermine synthase (spms-2) mutants during drought stress, combined with the quantitative expression of the entire polyamine biosynthetic pathway in the wild-type, has revealed a strong metabolic canalization of putrescine to spermine induced by drought. Such canalization requires spermidine synthase 1 (SPDS1) and spermine synthase (SPMS) activities and, intriguingly, does not lead to spermine accumulation but to a progressive reduction in spermidine and spermine pools in the wild-type. Our results suggest the participation of the polyamine back-conversion pathway during the drought stress response rather than the terminal catabolism of spermine. The putrescine to spermine canalization coupled to the spermine to putrescine back-conversion confers an effective polyamine recycling-loop during drought acclimation. Putrescine to spermine canalization has also been revealed in the desiccation tolerant plant C. plantagineum, which conversely to Arabidopsis, accumulates high spermine levels which associate with drought tolerance. Our results provide a new insight to the polyamine homeostasis mechanisms during drought stress acclimation in Arabidopsis and resurrection plants.

Figure 1

Transcriptional regulation of genes acting in the polyamine (PA) biosynthetic pathway under drought stress in Arabidopsis. Four-week-old plants were exposed to gradual drought stress for several days. Real time RT-PCR measurement of transcript levels of PA biosynthetic genes ADC1, ADC2, SPDS1, SPDS2, SPMS, ACL5, SAMDC1, SAMDC2, Polyamine oxidase 2 AtPAO2, Deoxyhypusine synthase DHS, RD29A and RD22 was performed after 0, 2, 4 and 6 days of drought treatment. ADC, Arginine decarboxylase; ACL5, Acaulis 5; dcSAM, decarboxylated S-adenosylmethionine; SAMDC, S-adenosylmethionine decarboxylase; SPDS, Spermidine synthase; SPMS, Spermine synthase; PAO, Polyamine oxidase.

Figure 2

Polyamine profiles under drought stress in polyamine biosynthetic mutant and wild-type Arabidopsis plants. Free putrescine, spermidine and spermine levels were analyzed in Arabidopsis wild-type, adc1–3, adc2–3, spds1–2, spds2–3 and spms-2 mutants after 0, 2, 4, 6, 10 and 16 days of drought treatment. Values are the mean from three biological replicates ±standard deviation (SD). DW, dry weight.

Figure 3

ADC, SAMDC, DAO and SMO enzymatic activities under drought. Wild type Arabidopsis plants exposed to drought stress were used for the analysis of arginine decarboxylase (ADC), S-adenosylmethionine decarboxylase (SAMDC), diamine oxidase (DAO) and spermine oxidase (SMO) activities at different time points of 24 h drought treatment. Values are the mean from three biological replicates ±SD.

Figure 4

Free putrescine (Put), spermidine (Spd) and spermine (Spm) levels in C. plantagineum plants exposed to drought stress conditions for 0, 1, 2, 4, 8, 24, 72 and 96 hours. Values are the mean from three biological replicates ±SD. DW, dried weight.