Two Rice Authentic Histidine Phosphotransfer Proteins, OsAHP1 and OsAHP2, Mediate Cytokinin Signaling and Stress Responses in Rice    

Abstract

Cytokinin plays an important role in plant development and stress tolerance. Studies of Arabidopsis (Arabidopsis thaliana) have demonstrated that cytokinin acts through a two-component system that includes a histidine (His) kinase, a His phosphotransfer protein (HP), and a response regulator. Phylogenetic analyses have revealed the conservation of His kinases but lineage-specific expansion of HPs and response regulators in rice (Oryza sativa). However, whether the functions of rice HPs have diverged remains unknown. In this study, two rice authentic HPs (OsAHP1 and OsAHP2) were knocked down simultaneously via RNA interference (RNAi), and the transgenic OsAHP-RNAi plants exhibited phenotypes expected for a deficiency in cytokinin signaling, including dwarfism with reduced internode lengths, enhanced lateral root growth, early leaf senescence, and reduced tiller numbers and fertility under natural conditions. The OsAHP-RNAi seedlings were also hyposensitive to exogenous cytokinin. Furthermore, OsAHP-RNAi seedlings were hypersensitive to salt treatment but resistant to osmotic stress relative to wild-type plants. These results indicate that OsAHPs function as positive regulators of the cytokinin signaling pathway and play different roles in salt and drought tolerance in rice.

Regulation of Na+ fluxes in plants

“…In wheat, the HKTs NAX1 and NAX2 fulfill similar roles (Lindsay et al, 2004). Shi et al (2002) suggested a similar role in xylem Na + reabsorption for the SOS1 transporter (depending on the level of salinity stress) but the evidence for this is less convincing.…”

Rice sulfoquinovosyltransferase SQD2.1 mediates flavonoid glycosylation and enhances tolerance to osmotic stress

“…Abiotic stresses, such as drought and high salinity, negatively impact plant growth and agricultural productivity. Plants have evolved to cope with adverse environments by a variety of strategies at the molecular, metabolic, cellular, physiological, and morphological levels (Jiang, Belfield, Cao, Smith, & Harberd, ; Martínez‐Atienza & Quintero, ; Nakabayashi et al, ; Sun et al, ). For example, reactive oxygen species (ROS), including superoxide radicals O 2˙ − , hydrogen peroxide H 2 O 2 , and hydroxyl radicals ˙OH, are accumulated under stress conditions, including high salinity and drought (Mittler, ).…”

OsCYP71D8L as a key regulator involved in growth and stress response by mediating gibberellins and cytokinins homeostasis in rice

“…Overexpression of KNOTTED1-like results in high-CK and low-GA and inhibits root development by inducting OsIPT2 and OsIPT3 expression (Sakamoto et al, 2006). Similarly, down-regulation of CK signaling leads to reduced internode lengths and tiller number, and promoted lateral root growth (Sun et al, 2014). Thus, the appropriate GAs and CKs homeostasis is required for the normal growth and development in rice.…”

“…Overexpressing ISOPENTENYLTRANSFERASE could lead to high CKs levels and improve drought tolerance by coordinating source/sink relationships and nutrient metabolism in rice (Peleg et al, 2011; Reguera et al, 2013). Similarly, OsAHP1 and OsAHP2 function as positive regulators of the cytokinin signaling and are required for the regulation salt and drought tolerance in rice (Sun et al, 2014). These findings show that GA and CK play antagonistic roles in plant response to abiotic stresses, and manipulating GA and CK levels is an effective strategy to improve stress tolerance in rice.…”