Gßγ dimers mediate low K+ stress-inhibited root growth via modulating auxin redistribution in Arabidopsis.

In the investigation of heterotrimeric G protein-mediated signal transduction in planta, their roles in the transmittance of low K+ stimuli remain to be elucidated. Here, we found that the primary root growth of wild-type Arabidopsis was gradually inhibited with the decrease of external K+ concentrations, while the primary root of the mutants for G protein ß subunit AGB1 and γ subunits AGG1, AGG2 and AGG3 could still grow under low K+ conditions (LK). Exogenous NAA application attenuated primary root elongation in agb1 and agg1/2/3 but promoted the growth in wild-type seedlings under LK stress. Using ProDR5:GFP, ProPIN1:PIN1-GFP and ProPIN2:PIN2-GFP reporter lines, a diminishment in auxin concentration at the radicle apex and a reduction in PIN1and PIN2 efflux carrier abundance were observed in wild-type roots under LK, a phenomenon not recorded in the agb1 and agg1/2/3. Further proteolytic and transcriptional assessments revealed an enhanced degradation of PIN1 and a suppressed expression of PIN2 in the wild-type background under LK, contrasting with the stability observed in the agb1 and agg1/2/3 mutants. Our results indicate that the G protein ß and γ subunits play pivotal roles in suppressing of Arabidopsis root growth under LK by modulating auxin redistribution via alterations in PIN1 degradation and PIN2 biosynthesis.

Ethylene Acts as a Local and Systemic Signal to Mediate UV-B-Induced Nitrate Reallocation to Arabidopsis Leaves and Roots via Regulating the ERFs-NRT1.8 Signaling Module.

Nitrate is the preferred nitrogen source for plants and plays an important role in plant growth and development. Under various soil stresses, plants reallocate nitrate to roots to promote stress tolerance through the ethylene-ethylene response factors (ERFs)-nitrate transporter (NRT) signaling module. As a light signal, ultraviolet B (UV-B) also stimulates the production of ethylene. However, whether UV-B regulates nitrate reallocation in plants via ethylene remains unknown. Here, we found that UV-B-induced expression of ERF1B, ORA59, ERF104, and NRT1.8 in both Arabidopsis shoots and roots as well as nitrate reallocation from hypocotyls to leaves and roots were impaired in ethylene signaling mutants for Ethylene Insensitive2 (EIN2) and EIN3. UV-B-induced NRT1.8 expression and nitrate reallocation to leaves and roots were also inhibited in the triple mutants for ERF1B, ORA59, and ERF104. Deletion of NRT1.8 impaired UV-B-induced nitrate reallocation to both leaves and roots. Furthermore, UV-B promoted ethylene release in both shoots and roots by enhancing the gene expression and enzymatic activities of ethylene biosynthetic enzymes only in shoots. These results show that ethylene acts as a local and systemic signal to mediate UV-B-induced nitrate reallocation from Arabidopsis hypocotyls to both leaves and roots via regulating the gene expression of the ERFs-NRT1.8 signaling module.