The ABA Receptor PYL8 Promotes Lateral Root Growth by Enhancing MYB77-Dependent Transcription of Auxin-Responsive Genes

Abstract

The phytohormone abscisic acid (ABA) regulates plant growth, development, and abiotic stress responses. ABA signaling is mediated by a group of receptors known as the PYR1/PYL/RCAR family, which includes the pyrabactin resistance 1–like protein PYL8. Under stress conditions, ABA signaling activates SnRK2 protein kinases to inhibit lateral root growth after emergence from the primary root. However, even in the case of persistent stress, lateral root growth eventually recovers from inhibition. We showed that PYL8 is required for the recovery of lateral root growth, following inhibition by ABA. PYL8 directly interacted with the transcription factors MYB77, MYB44, and MYB73. The interaction of PYL8 and MYB77 increased the binding of MYB77 to its target MBSI motif in the promoters of multiple auxin-responsive genes. Compared to wild-type seedlings, the lateral root growth of pyl8 mutant seedlings and myb77 mutant seedlings was more sensitive to inhibition by ABA. The recovery of lateral root growth was delayed in pyl8 mutant seedlings in the presence of ABA, and the defect was rescued by exposing pyl8 mutant seedlings to the auxin IAA (3-indoleacetic acid). Thus, PYL8 promotes lateral root growth independently of the core ABA-SnRK2 signaling pathway by enhancing the activities of MYB77 and its paralogs, MYB44 and MYB73, to augment auxin signaling.

ABA receptor PYL9 promotes drought resistance and leaf senescence

“…ABA-activated SnRK2s phosphorylate transcription factors, such as ABA-responsive element-binding factors (ABFs), and these phosphorylated ABFs regulate the expression of ABA-responsive genes (15). In Arabidopsis, 14 PYLs function diversely and redundantly in ABA and drought-stress signaling (16)(17)(18)(19). Understanding how each…”

The spatio-temporal specificity of PYR1/PYL/RCAR ABA receptors in response to developmental and environmental cues

“…38 According to the literatures, it is proposed that the dimeric receptors act as the key targets for chemical modulation of vegetative ABA responses as well as the objective receptors for protein engineering, [5][6]39 while the monomeric ones prefer implicated in genetic-modify plant traits for abiotic stress tolerance 2 and also involved in root function regulation. [17][18]23 That the more sensitive of shoot growth than root growth in response to draft stress, is resulted from the insufficient ABA level in the former than the latter to restrict ethylene production. 11 It was shown that leaf ABA concentration ([ABA]) varied greatly as a result of plant growth under different levels of soil water deficit at moderate (60%) or high (90%) relative air humidity (RH).…”

“…11 It is well known that osmotic stress-derived ABA can reduce leaf hydraulic conductivity and shoot growth, thus reducing the transpiration rate in Arabidopsis leaves, [12][13][14] whereas it can maintain root water uptake by enhancing root growth and root hydraulic conductivity. 8,11,[15][16][17] Recently it is found that the single PYL8 ABA receptor play a key role in mediating ABA-controlled root growth and root response to moisture gradient, means hydrotropism, [17][18] while there is a obvious redundant characteristics of PYR1/PYL/RCAR ABA receptor family in stomatal aperture regulation. 9 A naphthalene sulfonamide ABA agonist pyrabactin, which activates seed ABA responses but fails to trigger substantial responses in vegetative tissues in Arabidopsis thaliana.…”

“…17 Even in the belowground, ABA exerted a different role in regulating primary root growth and lateral root growth under osmotic stress conditions. [20][21][22] It is known ABA has a much stronger effect on lateral root than on the primary root, suggesting that different signaling mechanisms underlying regulating these two types of roots growth.…”

“…21 While PYL8 mediates the ability of ABA to inhibit primary root growth through the PP2C-SnRK2 pathway, 18 it together with PYL9 promotes lateral root growth recovery from inhibition independently of the core signaling pathway by enhancing MYB77-dependent transcription of auxin-responsive genes. 17,23 The cell-specificities of PYR1/PYL/RCAR ABA receptors It has been shown that application ABA directly enhance plasma membrane water permeability of roots cortical cells 15 and guard cells, 24 while inhibit that of vascular bundle-sheath cells 12 and has not effect to that of mesophyll cells. 12,24 The core signaling component SnRK2.6 has been documented implicated in plasma membrane intrinsic proteins PIP2;1 activation through protein phosphorylation at Ser-121, thus increase in guard cell permeability to water.…”