CRYPTOCHROME 1a-mediated blue light perception regulates tomato seed germination via changes in hormonal balance and endosperm-degrading hydrolase dynamics.

MAIN CONCLUSION: Blue light exposure delays tomato seed germination by decreasing endosperm-degrading hydrolase activities, a process regulated by CRY1a-dependent signaling and the hormonal balance between ABA and GA. The germination of tomato seeds (Solanum lycopersicum L.) is tightly controlled by an internal hormonal balance, which is also influenced by environmental factors such as light. In this study, we investigated the blue light (BL)-mediated impacts on physiological, biochemical, and molecular processes during the germination of the blue light photoreceptor CRYPTOCHROME 1a loss-of-function mutant (cry1a) and of the hormonal tomato mutants notabilis (not, deficient in ABA) and procera (pro, displaying a GA-constitutive response). Seeds were germinated in a controlled chamber in the dark and under different intensities of continuous BL (ranging from 1 to 25 µmol m-2 s-1). In general, exposure to BL delayed tomato seed germination in a fluency rate-dependent way due to negative impacts on the activities of endosperm-degrading hydrolases, such as endo-ß-mannanase, ß-mannosidase, and α-galactosidase. However, not and pro mutants presented higher germination speed index (GSI) compared to WT despite the BL influence, associated with higher hydrolase activities, especially evident in pro, indicating that the ABA/GA hormonal balance is important to diminish BL inhibition over tomato germination. The cry1a germination percentage was higher than in WT in the dark but its GSI was lower under BL exposure, suggesting that functional CRY1a is required for BL-dependent germination. BL inhibits the expression of GA-biosynthetic genes, and induces GA-deactivating and ABA-biosynthetic genes. The magnitude of the BL influence over the hormone-related transcriptional profile is also dependent upon CRY1a, highlighting the complex interplay between light and hormonal pathways. These results contribute to a better understanding of BL-induced events behind the photoregulation of tomato seed germination.

Cryptochrome 1a depends on blue light fluence rate to mediate osmotic stress responses in tomato.

The participation of plant cryptochromes in water deficit response mechanisms has been highlighted in several reports. However, the role of tomato (Solanum lycopersicum L.) cryptochrome 1a (cry1a) in the blue light fluence-dependent modulation of the water deficit response remains largely elusive. The tomato cry1a mutant and its wild-type counterpart were grown in water (no stress) or PEG6000 (osmotic stress) treatments under white light (60 µmol m-2 s-1) or from low to high blue light fluence (1, 5, 10, 15 and 25 µmol m-2 s-1). We first demonstrate that under nonstress conditions cry1a regulates seedling growth by mechanisms that involve pigmentation, lipid peroxidation and osmoprotectant accumulation in a blue light-dependent manner. In addition, we further highlighted under osmotic stress conditions that cry1a increased tomato growth by reduced malondialdehyde (MDA) and proline accumulation. Although blue light is an environmental signal that influences osmotic stress responses mediated by tomato cry1a, specific blue light fluence rates are required during these responses. Here, we show that CRY1a manipulation may be a potential biotechnological target to develop a drought-tolerant tomato variety. Nevertheless, the complete understanding of this phenomenon requires further investigation.

Constitutive gibberellin response in grafted tomato modulates root-to-shoot signaling under drought stress.

Plants are sessile organisms that must perceive and respond to various environmental constraints throughout their life cycle. Among these constraints, drought stress has become the main limiting factor to crop production around the world. Water deprivation is perceived primarily by the roots, which efficiently signal the shoot to trigger drought responses in order to maximize a plant's ability to survive. In this study, the tomato (Solanum lycopersicum L.) mutant procera (pro), with a constitutive response to gibberellin (GA), and its near isogenic line cv. Micro-Tom (MT), were used in reciprocal grafting under well-watered and water stress conditions to evaluate the role of GA signaling in root-to-shoot communication during drought stress. Growth, oxidative stress, gene expression, water relations and hormonal content were measured in order to provide insights into GA-mediated adjustments to water stress. All graft combinations with pro (i.e. pro/pro, MT/pro and pro/MT) prevented the reduction of growth under stress conditions without a reduction in oxidative stress. The increase of oxidative stress was followed by upregulation of SlDREB2, a drought-tolerance related gene, in all drought-stressed plants. Scions harboring the pro mutation tended to increase the abscisic acid (ABA) content, independent of the rootstock. Moreover, the GA sensitivity of the rootstock modulated stomatal conductance and water use efficiency under drought stress, indicating GA and ABA crosstalk in the adjustment of growth and water economy.