Abstract
Desiccation tolerance is a complex phenomenon that depends on the regulated expression of numerous genes during dehydration and subsequent rehydration. Our previous study identified a chloroplast drought-induced stress protein (MaCDSP32) in mulberry, a thioredoxin (Trx) that is upregulated under drought conditions and is likely to confer drought tolerance to transgenic plants. Mulberry (Morus spp.) is an ecologically and economically important perennial woody plant that is widely used in forest management to combat desertification. However, its stress tolerance physiology is not well understood. In this study, the functions of MaCDSP32 gene were investigated. The expression of MaCDSP32 exhibited a circadian rhythm and was induced by mild and severe water deficits. Under abiotic stress, MaCDSP32-overexpressing plants exhibited increased stress sensitivity with lower water retention capacity and more severe lipid peroxidation than the wild-type (WT) plants. Furthermore, the activity of superoxide dismutase (SOD), the contents of proline and soluble sugars and the expression of stress-related transcription factors were lower in the MaCDSP32-overexpressing plants than in the WT plants. However, the MaCDSP32-overexpressing lines exhibited stronger recovery capability after rewatering post-drought. Moreover, the SOD enzyme activity, proline content, and soluble sugar content were higher in the transgenic plants after rewatering than in the WT plants. The production of the reactive oxygen species (ROS) H2O2 and O2– was significantly lower in the transgenic plants than in the WT plants. In addition, under abiotic stress, the MaCDSP32-overexpressing lines exhibited improved seed germination and seedling growth, these effects were regulated by a positive redox reaction involving MaCDSP32 and one of its targets. In summary, this study indicated that MaCDSP32 from mulberry regulates plant drought tolerance and ROS homeostasis mainly by controlling SOD enzyme activity and proline and soluble sugar concentrations and that this control might trigger the stress response during seed germination and plant growth. Overall, MaCDSP32 exerts pleiotropic effects on the stress response and stress recovery in plants.
Highlights
Plants, as sessile organisms, are constantly facing challenges from their surroundings and have evolved a set of precise defense mechanisms and self-repair systems during the long process of survival of the fittest (Zhu, 2016)
The amino acid sequence of MaCDSP32 showed the highest similarity with the protein sequences from Morus notabilis (XM 010101817.1), Gas Exchange Parameters and Photosynthetic Pigments Related to Photosynthesis
Lower H2O2 production and higher O2− production were found in transgenic tobacco lines than in the WT plants under both stress conditions, which indicated that MaCDSP32 is involved in reactive oxygen species (ROS) metabolism in response to abiotic stress
Summary
As sessile organisms, are constantly facing challenges from their surroundings and have evolved a set of precise defense mechanisms and self-repair systems during the long process of survival of the fittest (Zhu, 2016). It is important to maintain the normal physiological functions of some response proteins in plants under stress (Vieira Dos Santos and Rey, 2006). Trx-x, Trx-y and CDSP32 are Trxs that play important roles in the responses of chloroplast to oxidative stress (Foyer, 2018). These Trxs can be reduced by two pathways, which show some overlap with regard to their target proteins: the ferredoxindependent Trx system and the NADPH-dependent Trx reductase (NTRC) pathway These two systems function together with 2Cys Prxs. It is clear that Trxs play a fundamental role in regulating diverse processes in living cells (Montrichard et al, 2009), further studies are needed to determine the specific enzymes targeted by certain Trxs and their interaction regulatory processes in chloroplasts under different abiotic stresses
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