Cytosolic proline is required for basal freezing tolerance in Arabidopsis

Abstract

The amino acid proline accumulates in many plant species under abiotic stress conditions, and various protective functions have been proposed. During cold stress, however, proline content in Arabidopsis thaliana does not correlate with freezing tolerance. Freezing sensitivity of a starchless plastidic phosphoglucomutase mutant (pgm) indicated that localization of proline in the cytosol might stabilize the plasma membrane during freeze–thaw events. Here, we show that re‐allocation of proline from cytosol to vacuole was similar in the pyrroline‐5‐carboxylate synthase 2–1 (p5cs2–1) mutant and the pgm mutant and caused similar reduction of basal freezing tolerance. In contrast, the starch excess 1–1 mutant (sex1‐1) had even lower freezing tolerance than pgm but did not affect sub‐cellular localization of proline. Freezing sensitivity of sex1‐1 mutants affected primarily the photosynthetic electron transport and was enhanced in a sex1‐1::p5cs2–1 double mutant. These findings indicate that several independent factors determine basal freezing tolerance. In a pgm::p5cs2–1 double mutant, freezing sensitivity and proline allocation to the vacuole were the same as in the parental lines, indicating that the lack of cytosolic proline was the common cause of reduced basal freezing tolerance in both mutants. We conclude that cytosolic proline is an important factor in freezing tolerance of non‐acclimated plants.

Combined Transcriptome and Metabolome Profiling Provide Insights into Cold Responses in Rapeseed (Brassica napus L.) Genotypes with Contrasting Cold-Stress Sensitivity

“…Moreover, an earlier study on coffee genotypes with different cold sensitivities reported higher expression of sugar contents and respiratory enzyme activities [ 37 ]. Particularly, the better growth of GX74 and respective higher expressions of HKs and PGM is consistent with the earlier reports on Jatropha curcas [ 38 ] and Arabidopsis [ 39 ]. Additionally, the XYL4 gene has been previously highlighted as an important gene in abiotic stress tolerance in alfalfa [ 40 ]; thus, it may also function similarly in rapeseed.…”

Comprehensive transcriptome analysis reveals heat-responsive genes in flowering Chinese cabbage (Brassica campestris L. ssp. chinensis) using RNA sequencing

“…The Sid2-1 mutant was reported in Arabidopsis, significantly increasing soluble sugars to improve drought and heat stress (Kumazaki and Suzuki, 2019). Similarly, heat stress increased proline content in leaves of soybean (Amirjani, 2010), tomato (Rivero et al, 2004), chickpea (Chakraborty and Tongden, 2005), and Arabidopsis (Zhang and Huang, 2013;Gurrieri et al, 2020;Hoermiller et al, 2022). The cluster 2 DEGs (Figure 4; Table S2) are associated with late embryogenesis abundant protein (Magwanga et al, 2018) and ubiquitin (Qian et al, 2020a), which protect sub-cellular and cellular structures from dehydration and oxidative forces.…”

Limitation of sucrose biosynthesis shapes carbon partitioning during plant cold acclimation

“…This indicates a significant cold‐induced reprogramming of plant metabolism to stabilize a new metabolic homeostasis and to prevent irreversible tissue damage (Kosová et al, 2011). Previous studies have shown that regulation of carbon allocation and flux partitioning between compartments, for example, chloroplasts and cytosol, plays a central role in cold acclimation because it enables compartment‐specific accumulation of osmotically active and cryoprotective substances (Fürtauer et al, 2016; Hoermiller et al, 2017; Hoermiller et al, 2022; Lundmark et al, 2006). To reveal if and how deficiencies in starch and flavonoid metabolism may affect carbon partitioning during cold acclimation, substrate saturated enzyme activities, that is, v max , of the central carbohydrate metabolism were quantified at different temperatures ranging from ambient (22°C) to low (4°C) temperature.…”