Auxin plays a role in the adaptation of rice to anaerobic germination and seedling establishment

Abstract

Auxin is well known to stimulate coleoptile elongation and rapid seedling growth in the air.However, its role in regulating rice germination and seedling establishment under submergence is largely unknown. Previous studies have shown that excessive levels of IAA frequently cause the inhibition of plant growth and development. In the present study, the high-level accumulation of endogenous IAA is observed under submergence in the dark, stimulating rice coleoptile elongation but limiting the root and primary leaf growth during anaerobic germination (AG). We found that oxygen and light can reduce IAA levels, promote the seedling establishment and enhance rice AG tolerance. miRNA microarray profiling and RNA gel blot analysis results show that the expression of miR167 is negatively regulated by submergence; it subsequently modulates the accumulation of free IAA through the miR167-ARF-GH3 pathway. The OsGH3-8 encodes an IAA-amido synthetase that functions to prevent free IAA accumulation. Reduced miR167 levels or overexpressing OsGH3-8 increase auxin metabolism, reduce endogenous levels of free IAA and enhance rice AG tolerance. The present study reveals that poor seed germination and seedling growth inhibition resulting from excessive IAA accumulation would cause intolerance to submergence in rice, suggesting that a certain threshold level of auxin is essential for rice AG tolerance.

Zn nutrients-loaded chitosan nanocomposites and their efficacy as nanopriming agents for maize (Zea mays) seeds

“…Another related study showed that nanopriming of O. sativa seeds with the 375 nm CS/TPP NPs (50 μg/mL) resulted in increased germination percentage and seedling vigour index in 7-day-old seedlings in normal growth conditions and under salt stress ( Soni et al, 2023 ). It has been inferred that adsorption of chitosan NPs onto seeds could initiate the biosynthesis of auxin, which stimulates coleoptile elongation ( Lee et al, 2022 ). Furthermore, Hameed et al (2020) reported that treatment of O. sativa seeds with Zn NPs-stabilized chitosan-polyvinyl alcohol (0.16%) elicited the biosynthesis of proteins and upregulated the activities of protease and α-amylase enzymes in comparison with the unprimed seeds.…”

Flooding Tolerance of Rice: Regulatory Pathways and Adaptive Mechanisms

“…Submergence downregulates the expression of miR393, thus activating the auxin signaling pathway and stimulating coleoptile elongation in rice [40]. Interestingly, a recent report has shown that a certain threshold level of endogenous auxin is required for rice germination and early seedling growth during submergence [41]. Lee and his co-workers showed that a submergence-repressed miR167 is involved in the metabolic regulation of IAA through the miR167a-ARF-GH3 pathway [41].…”

“…Interestingly, a recent report has shown that a certain threshold level of endogenous auxin is required for rice germination and early seedling growth during submergence [41]. Lee and his co-workers showed that a submergence-repressed miR167 is involved in the metabolic regulation of IAA through the miR167a-ARF-GH3 pathway [41]. MiR167-directed ARF mRNA cleavage is accompanied by the downregulation of glycoside hydrolase 3 (GH3) [42].…”

“…GH3-8 encodes an IAA-amido synthetase that prevents free IAA accumulation and maintains auxin homeostasis [43]. Reduced miR167 levels or increased GH3-8 levels reduce the endogenous levels of free IAA, thus promoting rice AG/AGD [41]. Recently, OsPIN2, a gene encoding an auxin efflux transporter, was found to negatively regulate hypoxia tolerance by affecting auxin transport and ROS accumulation [44].…”

Prospects for rice in 2050

“…This review should facilitate the manipulation of key genes for better performance under flood conditions in rice. Lee et al (2022) reported that auxin is also necessary for rice to adapt to anaerobic germination and seedling establishment; they showed that reduced endogenous IAA enhances rice anaerobic germination tolerance and promotes seedling establishment in rice while excessive accumulation of IAA leads to poor seed germination and seedling establishment, suggesting that there is a certain threshold value for auxin to function in anaerobic germination and seedling establishment (Lee et al, 2022).…”