The mitogen-activated protein kinase (MAPK) cascade is an evolutionarily conserved signal transduction module involved in transducing extracellular signals to the nucleus for appropriate cellular adjustment. This cascade essentially consists of three components: a MAPK kinase kinase (MAPKKK), a MAPK kinase, and a MAPK, connected to each other by the event of phosphorylation. Here, we report the characterization of a MAPKKK, ABA-INSENSITIVE PROTEIN KINASE1 (AIK1), which regulates abscisic acid (ABA) responses in Arabidopsis (Arabidopsis thaliana). T-DNA insertion mutants of AIK1 showed insensitivity to ABA in terms of both root growth and stomatal response. AIK1 functions in ABA responses via regulation of root cell division and elongation, as well as stomatal responses. The activity of AIK1 is induced by ABA in Arabidopsis and tobacco (Nicotiana benthamiana), and the Arabidopsis protein phosphatase type 2C, ABI1, a negative regulator of ABA signaling, restricts AIK1 activity by dephosphorylation. Bimolecular fluorescence complementation analysis showed that MPK3, MPK6, and AIK1 interact with MKK5. The single mutant seedlings of mpk6 and mkk5 have similar phenotypes to aik1, but mkk4 does not. AIK1 was localized in the cytoplasm and shown to activate MKK5 by protein phosphorylation, which was an ABA-activated process. Constitutively active MKK5 in aik1 mutant seedlings complements the ABA-insensitive root growth phenotype of aik1. The activity of MPK6 was increased by ABA in wild-type seedlings, but its activation by ABA was impaired in aik1 and aik1 mkk5 mutants. These findings clearly suggest that the AIK1-MKK5-MPK6 cascade functions in the ABA regulation of primary root growth and stomatal response.

Primary root growth in cereal crops is fundamental for early establishment of the seedling and grain yield. In young rice (Oryza sativa) seedlings, the primary root grows rapidly for 7–10 days after germination and then stops; however, the underlying mechanism determining primary root growth is unclear. Here, we report that the interplay of ethylene and gibberellin (GA) controls the orchestrated development of the primary root in young rice seedlings. Our analyses advance the knowledge that primary root growth is maintained by higher ethylene production, which lowers bioactive GA contents. Further investigations unraveled that ethylene signaling transcription factor ETHYLENE INSENSITIVE3-LIKE 1 (OsEIL1) activates the expression of the GA metabolism genes GIBBERELLIN 2-OXIDASE 1 (OsGA2ox1), OsGA2ox2, OsGA2ox3, and OsGA2ox5, thereby deactivating GA activity, inhibiting cell proliferation in the root meristem, and ultimately gradually inhibiting primary root growth. Mutation in OsGA2ox3 weakened ethylene-induced GA inactivation and reduced the ethylene sensitivity of the root. Genetic analysis revealed that OsGA2ox3 functions downstream of OsEIL1. Taken together, we identify a molecular pathway impacted by ethylene during primary root elongation in rice and provide insight into the coordination of ethylene and GA signals during root development and seedling establishment.

The plant glutathione peroxidase (GPX) family consists of multiple isoenzymes with distinct subcellular locations, tissue-specific expression patterns and environmental stress responses. In this study, 13 putative GPXs from the genome of Gossypium hirsutum (GhGPXs) were identified and a conserved pattern among plant GPXs were exhibited, besides this they also responded to multiple environmental stresses and we predicted that they had hormone responsive cis-elements in their promoter regions. Most of the GhGPXs on expression in yeast can scavenge H₂O₂. Our results showed that different members of the GhGPX gene family were co-ordinately regulated under specific environmental stress conditions, and suggested the importance of GhGPXs in hormone treatments and abiotic stress responses.

The ubiquitin-binding protein OsDSK2a modulates the level of the gibberellin metabolism regulator EUI to coordinate plant growth and salt-stress responses in ri

Tissue-specific differentiation of phosphorus transporters coordinated with their regulators confers phosphorus homeostasis, regulating nodule development.