Alkaline Stress Induces Different Physiological, Hormonal and Gene Expression Responses in Diploid and Autotetraploid Rice

Abstract

Saline−alkaline stress is a critical abiotic stress that negatively affects plants’ growth and development. Considerably higher enhancements in plant tolerance to saline−alkaline stress have often been observed in polyploid plants compared to their diploid relatives, the underlying mechanism of which remains elusive. In this study, we explored the variations in morphological and physiological characteristics, phytohormones, and genome-wide gene expression between an autotetraploid rice and its diploid relative in response to alkaline stress. It was observed that the polyploidization in the autotetraploid rice imparted a higher level of alkaline tolerance than in its diploid relative. An eclectic array of physiological parameters commonly used for abiotic stress, such as proline, soluble sugars, and malondialdehyde, together with the activities of some selected antioxidant enzymes, was analyzed at five time points in the first 24 hours following the alkaline stress treatment between the diploid and autotetraploid rice. Phytohormones, such as abscisic acid and indole-3-acetic acid were also comparatively evaluated between the two types of rice with different ploidy levels under alkaline stress. Transcriptomic analysis revealed that gene expression patterns were altered in accordance with the variations in the cellular levels of phytohormones between diploid and autotetraploid plants upon alkaline stress. In particular, the expression of genes related to peroxide and transcription factors was substantially upregulated in autotetraploid plants compared to diploid plants in response to the alkaline stress treatment. In essence, diploid and autotetraploid rice plants exhibited differential gene expression patterns in response to the alkaline stress, which may shed more light on the mechanism underpinning the ameliorated plant tolerance to alkaline stress following genome duplication.

Insights into the regulation of wild soybean tolerance to salt-alkaline stress

“…Phytohormones, especially ABA, play key roles in regulating plant tolerance to salt-alkaline stress. Current research has well-illustrated the core components of the hormone signal transduction pathway in plants and has demonstrated the regulation of hormone signaling genes on the tolerance to salt-alkaline stress ( Fang et al., 2021 ; Wang N. et al., 2022b ). In G. soja , several genes were characterized to modulate salt-alkaline tolerance via hormone-dependent signaling pathways.…”

Comparative Analysis of Physiological, Hormonal and Transcriptomic Responses Reveal Mechanisms of Saline-Alkali Tolerance in Autotetraploid Rice (Oryza sativa L.)

“…The 93-11T was developed from tissue culture of 93-11D and artificially synthesized by colchicine treatment [59], and self-pollinated for four generations to ensure genetic stability. Chromosomes were counted as previously described [49]. Seeds of 93-11D and 93-11T were sterilized by 10% sodium hypochlorite (NaOCl) for 15 min and rinsed three times with distilled water, then soaked in tap water for 1 d at 35 • C in the dark.…”

“…The measurements of soluble sugar, proline and MDA content, as well as SOD and POD activities in leaves (93-11D and 93-11T) at 0, 3, 6, 12 and 24 hpt were conducted as previously described [49]. Briefly, (i) soluble sugar content: 5 mL of anthrone reagent were added to 1 mL of extract, incubated at 95 • C for 15 min.…”

“…Briefly, leaf samples (50 mg) were ground with liquid nitrogen, the chloroform was added to separate the different phases, the sublayer mixture was subsequently re-suspended with pre-chilled 80% methanol. The supernatant was assayed using an ACQUITY UHPLC system (Waters Corporation, Milford, MA, USA) coupled with an SCIEX Triple Quad™ 5500 + LC-MS/MS system (AB SCIEX, Framingham, MA, USA) [49]. All the processes were performed by Lu Ming Biotechnology Co., Ltd. (Shanghai, China).…”

“…Upon salt (NaCl) stress, increased expression of stress-responsive genes can induce hypermethylation and inhibit transposable elements adjacent to stress-responsive genes in tetraploid rice [48]. Recently, autotetraploid rice exhibited stronger tolerance to alkaline (NaOH) stress than diploid rice, which was manifested in differences in phenotypes, physiological properties, hormone levels and gene expression patterns [49]. Accordingly, still limited research has been performed to elucidate the physiological and molecular mechanisms of polyploid rice in response to saline/saline-alkali stress.…”