Abstract
The primary root is the basic component of the root system and plays a key role in early seedling growth in rice. Its growth is easily affected by environmental cues, such as salt stress. Abscisic acid (ABA) plays an essential role in root development, but the molecular mechanism underlying ABA-regulated root growth in response to salt stress remains poorly understood. In this study, we report that salt stress inhibits primary root elongation and promotes primary root swelling. Moreover, salt stress induces the expression of ABA-responsive genes and ABA accumulation in the primary root, revealing that ABA plays an essential role in salt-modulated root growth. Transgenic lines of OsSAPK10-OE and OsABIL2-OE, which constitutively express OsSAPK10 or OsABIL2, with enhanced or attenuated ABA signaling, show increased and decreased sensitivity to salt, correspondingly. Microscopic analysis indicates that salt and ABA inhibits cell proliferation and promotes cell expansion in the root apical meristem. Transcriptome analysis showed that ABA induces the expression of EXPANSIN genes. Further investigations indicate that ABA exerts these effects largely through ABA signaling. Thus, our findings deepen our understanding of the role of ABA in controlling primary root growth in response to salt stress, and this knowledge can be used by breeders to cultivate rice varieties suitable for saline–alkali land.
Highlights
Salt stress significantly inhibited primary root elongation and promoted root swelling, and the effect increased with increasing salt concentrations (Figure 1A–D), suggesting that salt stress has a dual role in rice primary root growth, i.e., the restriction of primary root elongation and the swelling of the root tip
We asked whether salt-regulated root growth in rice requires the function of Abscisic acid (ABA)
We detected the expression of ABA-responsive genes [34] and ABA content in primary roots with or without salt treatment
Summary
Roots anchor plants and take up water and nutrients from the soil. Root development strongly affects plant growth and productivity [1]. Salinity stress is one of the major constraints on plant growth, affecting rice productivity worldwide, and roots are the primary target site for perception of salt stress signals which could act as an early warning system for the plant [4,5]. The primary root initiates during embryogenesis and develops shortly after germination, and plays a key role in seedling establishment [7]. The growth of the primary root is maintained by cell proliferation in the root apical meristem (RAM) and cell elongation in the elongation zone, plant hormones playing an important role in this process [8,9,10]
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