Abstract
Abiotic stresses, such as salt and heat stress, coexist in some regions of the world and can have a significant impact on agricultural plant biomass and production. Rice is a valuable crop that is susceptible to salt and high temperatures. Here, we studied the role of flavanol 3-hydroxylase in response to combined salt and heat stress with the aim of better understanding the defensive mechanism of rice. We found that, compared with wild-type plants, the growth and development of transgenic plants were improved due to higher biosynthesis of kaempferol and quercetin. Furthermore, we observed that oxidative stress was decreased in transgenic plants compared with that in wild-type plants due to the reactive oxygen species scavenging activity of kaempferol and quercetin as well as the modulation of glutathione peroxidase and lipid peroxidase activity. The expression of high-affinity potassium transporter (HKT) and salt overly sensitive (SOS) genes was significantly increased in transgenic plants compared with in control plants after 12 and 24 h, whereas sodium-hydrogen exchanger (NHX) gene expression was significantly reduced in transgenic plants compared with in control plants. The expression of heat stress transcription factors (HSFs) and heat shock proteins (HSPs) in the transgenic line increased significantly after 6 and 12 h, although our understanding of the mechanisms by which the F3H gene regulates HKT, SOS, NHX, HSF, and HSP genes is limited. In addition, transgenic plants showed higher levels of abscisic acid (ABA) and lower levels of salicylic acid (SA) than were found in control plants. However, antagonistic cross talk was identified between these hormones when the duration of stress increased; SA accumulation increased, whereas ABA levels decreased. Although transgenic lines showed significantly increased Na+ ion accumulation, K+ ion accumulation was similar in transgenic and control plants, suggesting that increased flavonoid accumulation is crucial for balancing Na+/K+ ions. Overall, this study suggests that flavonoid accumulation increases the tolerance of rice plants to combined salt and heat stress by regulating physiological, biochemical, and molecular mechanisms.
Highlights
The increase in global warming is causing a worldwide increase in abiotic stress to plants, including an increase in its intensity and duration, which can have a devastating effect on the growth, yield, and quality of crops (Pandey et al, 2017)
We focused on flavanol 3-hydroxylase, which plays a key role in flavonoid biosynthesis and abiotic stress mitigation
Shoot length was reduced in the transgenic line when compared to Wt-control plants, the reduction was less than that in wild-type treated (Wt-t) plants, indicating that F3H overexpression is involved in plant growth and development
Summary
The increase in global warming is causing a worldwide increase in abiotic stress to plants, including an increase in its intensity and duration, which can have a devastating effect on the growth, yield, and quality of crops (Pandey et al, 2017). Drought, and high temperature are common abiotic stresses that cause many physiological and molecular changes in plants that can lead to yield losses (Ahuja et al, 2010). Many researchers have studied the responses of plants to abiotic stresses, thereby increasing our knowledge on the subject. Salinity and high temperature are two of the main constraints for the growth of food resources; adaptation strategies are required for the development of agronomic traits that increase the stress tolerance of plants (Francini and Sebastiani, 2019). Development of transgenic plant is a powerful tool to address various agronomic traits including breeding increased tolerance against biotic stress and abiotic stress (Lavania et al, 2015)
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