Ethylene inhibits rice root elongation in compacted soil via ABA- and auxin-mediated mechanisms

Abstract

Soil compaction represents a major agronomic challenge, inhibiting root elongation and impacting crop yields. Roots use ethylene to sense soil compaction as the restricted air space causes this gaseous signal to accumulate around root tips. Ethylene inhibits root elongation and promotes radial expansion in compacted soil, but its mechanistic basis remains unclear. Here, we report that ethylene promotes abscisic acid (ABA) biosynthesis and cortical cell radial expansion. Rice mutants of ABA biosynthetic genes had attenuated cortical cell radial expansion in compacted soil, leading to better penetration. Soil compaction-induced ethylene also up-regulates the auxin biosynthesis gene OsYUC8 . Mutants lacking OsYUC8 are better able to penetrate compacted soil. The auxin influx transporter OsAUX1 is also required to mobilize auxin from the root tip to the elongation zone during a root compaction response. Moreover, osaux1 mutants penetrate compacted soil better than the wild-type roots and do not exhibit cortical cell radial expansion. We conclude that ethylene uses auxin and ABA as downstream signals to modify rice root cell elongation and radial expansion, causing root tips to swell and reducing their ability to penetrate compacted soil.

Soilborne bacterium Klebsiella pneumoniae promotes cluster root formation in white lupin through ethylene mediation

“…Recently, Huang et al . (2022) reported that root ethylene accumulation resulted in increased auxin response in the meristematic and elongation zones of root epidermal cells in rice. The addition of NAA restored root elongation inhibition in ethylene‐insensitive mutants ( oseil1 and oseil2 ) under compacted soil conditions.…”

“…Early studies on rice suggested that ethylene could induce YUC8 transcription, encoding an enzyme that converts indole-3-pyruvic acid to IAA to increase IAA biosynthesis and thus restricting primary root elongation (Qin et al, 2017). Recently, Huang et al (2022) reported that root ethylene accumulation resulted in increased auxin response in the meristematic and elongation zones of root epidermal cells in rice. The addition of NAA restored root elongation inhibition in ethyleneinsensitive mutants (oseil1 and oseil2) under compacted soil conditions.…”

Recent Advances in the Bacterial Phytohormone Modulation of Plant Growth

“…Higher ethylene levels are typically found in ripening fruit while much lower levels are associated with early vegetative development, seed germination, tissue differentiation, formation of root and shoot primordia, root branching and elongation, lateral bud development, pollen tube growth, flowering initiation, anthocyanin synthesis, flower opening and senescence, VOC synthesis, leaf and fruit senescence, Rhizobia nodule formation, mycorrhizae–plant interaction, and the response of plants to various biotic and abiotic stresses [ 83 , 84 , 85 ]. It was recently postulated that ethylene regulates growth responses using different signaling pathways, such as auxins and abscisic acid (ABA), whose responses can reduce the ability of roots to penetrate the soil, mainly in compacted soils [ 86 ].…”

Functional implications of multiseriate cortical sclerenchyma for soil resource capture and crop improvement

“…The composition and size of cortical cells have been shown to be important for soil penetration in hard soils ( Chimungu et al 2015 ; Colombi and Walter 2016 ; Huang et al 2022 ). Several physical soil properties such as water content, texture and bulk density influence mechanical impedance ( Gao et al 2016 ; Vanhees et al 2020 ) and can limit root elongation, crop growth and, subsequently, crop yield ( Whalley et al 2005 ; Whitmore and Whalley 2009 ; Bengough et al 2011 ; Gao et al 2016 ).…”

“…Roots also sense mechanical impedance through ethylene, as soil compaction reduces gas diffusion through a reduction in the number and size of air-filled pores. This accumulation of ethylene at the root tip in compacted soil triggers a suite of hormones that restrict root growth ( Jacobsen et al 2021 ; Pandey et al 2021 ; Huang et al 2022 ). Multiseriate cortical sclerenchyma and this ethylene ‘stop signal’ suggest that there may be several strategies of plants to optimize root forage in soils with greater mechanical impedance.…”