Neighbour signals perceived by phytochrome B increase thermotolerance in Arabidopsis

Abstract

Due to the preeminence of reductionist approaches, understanding of plant responses to combined stresses is limited. We speculated that light-quality signals of neighbouring vegetation might increase susceptibility to heat shocks because shade reduces tissue temperature and hence the likeness of heat shocks. In contrast, plants of Arabidopsis thaliana grown under low-red/far-red ratios typical of shade were less damaged by heat stress than plants grown under simulated sunlight. Neighbour signals reduce the activity of phytochrome B (phyB), increasing the abundance of PHYTOCHROME-INTERACTING FACTORS (PIFs). The phyB mutant showed high tolerance to heat stress even under simulated sunlight, and a pif multiple mutant showed low tolerance under simulated shade. phyB and red/far-red ratio had no effects on seedlings acclimated with nonstressful warm temperatures before the heat shock. The phyB mutant showed reduced expression of several fatty acid desaturase (FAD) genes and less proportion of fully unsaturated fatty acids and electrolyte leakage of membranes exposed to heat shocks. Red-light-activated phyB also reduced thermotolerance of dark-grown seedlings but not via changes in FADs expression and membrane stability. We propose that the reduced photosynthetic capacity linked to thermotolerant membranes would be less costly under shade, where the light input limits photosynthesis.

Light acts as a stressor and influences abiotic and biotic stress responses in plants

“…phyB also acts as a molecular switch to turn on/off several heat stress response genes under different light conditions resulting in thermotolerance (Song, Liu, Hu, & Wu, 2017). Low red to far‐red ratios (R:FR) reduce the activity of phyB, thereby increasing the abundance of PIFs resulting in a higher tolerance to heat (Arico et al, 2019). In addition, these shade conditions decrease the transcript levels of FATTY ACID DESATURASES ( FADs ) resulting in a shift in fatty acid composition towards more saturated fatty acids.…”

“…During heat stress, the produced ROS promote peroxidation of unsaturated fatty acids (Anjum, Khan, Sofo, Baier, & Kizek, 2016). By reducing the targets of oxidative damage, thermotolerance increases (Arico et al, 2019). An overview of the crosstalk between light and thermotolerance is given in Figure 7.…”

Phytochrome type B family: The abiotic stress responses signaller in plants

“…Such evidence was also supported by Song, Liu, Hu, and Wu (2017) in Arabidopsis phyB mutant seedlings that exhibited a higher survival rate and lateral root length after heat stress treatment compared to WT seedlings. These responses, shown by phyB mutants, were directly related to an increase in PIF accumulation, since Arico et al (2019) demonstrated that the thermotolerance acquired by Arabidopsis phyB mutants (lower proportion of damaged plants after heat shock) was not pronounced in pifq mutants ( pif1, pif3, pif4 and pif5 ), which exhibited no difference from WT plants. In contrast to cold stressed plants, heat stressed plants decreased the levels of USFA, which can reduce the targets of oxidative damage (double bonds between C‐atoms) and increase the thermotolerance to heat stress (Das & Roychoudhury, 2014).…”

“…Thus, it is not surprising that phys were previously described to regulate responses to diverse abiotic and biotic stresses (Carvalho, Campos, & Azevedo, 2011), such as salt stress (Indorf, Cordero, Neuhaus, & Rodríguez‐Franco, 2007), drought stress (Kraepiel et al, 1994), low and high‐temperature stress (Williams, Pellett, & Klein, 1972; Foreman et al, 2011) and high light (Wellmann, Schneider‐Zeibert, & Beggs, 1984). Highlighting the phy type B family shows some similar responses among species and many research groups have targeted their efforts to understand phyB‐modulated stress responses, because such responses could be altered in the same species, e.g., phyB1 and phyB2 gene duplication controlling different stress acclimation responses (Arico et al, 2019; Gavassi, Monteiro, Campos, Melo, & Carvalho, 2017; Kreslavski et al, 2015; Kwon et al, 2018; Yoo et al, 2017). Therefore, in this review, we summarised the phyB‐modulated stress responses to elucidate future research for plant breeding.…”

Aureochromes are necessary for maintaining polyunsaturated fatty acid content inNannochloropsis oceanica

“…In the cyanobacterium Synechocystis PCC 6803 the induction of the transcription of fatty acid desaturase genes is dependent on photosynthesis (Kis et al, 1998). Phytochrome B is necessary for expression of fatty acid desaturases in the land plant Arabidopsis thaliana and shade (low red/far-red ratio) has a negative impact on fatty acid desaturation (Arico et al, 2019). Unsaturated fatty acids are mainly present in glycerolipids localized in photosynthetic membranes (Li-Beisson et al, 2019) and light signals could ensure the chloroplast growth necessary to sustain cellular growth.…”