79. Which one of the following amino acids is
characteristics of and is conserved in response regulator of plant two component systems?
(1) Aspartic acid
(2) Glutamic acid

(3) Tyrosine
(4) Histidine

Conserved Amino Acid in Plant Two-Component System Response Regulators: Aspartic Acid

Introduction

Plant two-component systems (TCS) are crucial signaling pathways that allow plants to perceive and respond to environmental stimuli and hormones such as cytokinins. These systems typically comprise a sensor histidine kinase and a response regulator (RR). The RR protein contains a conserved amino acid residue that accepts a phosphate group, which activates the RR and drives downstream responses.

Key Conserved Residue: Aspartic Acid

The response regulator receives the phosphoryl group from the histidine kinase on a highly conserved aspartic acid (Asp) residue located in the receiver domain of the RR protein. This phosphorylation triggers conformational changes activating the response regulator’s function, often as a transcription factor modulating gene expression.

• The histidine kinase autophosphorylates a conserved histidine residue.

• The phosphate is transferred to the conserved aspartic acid residue in the RR.

• This phosphotransfer is essential for activating the RR and propagating the signal.

Importance and Conservation

• Aspartic acid is the characteristic and conserved amino acid in both bacterial and plant response regulators.

• This residue’s phosphorylation state determines the activity status of the RR.

• The presence of this conserved Asp highlights the evolutionary conservation of the TCS phosphorelay mechanism across kingdoms.

Supporting Evidence

Scientific literature (e.g., [Stock et al., 2000]; [Lohrmann and Harter, 2002]; [Sun et al., 2014]) explains the central role of aspartic acid in receiving and relaying the phosphorylation signal in plant response regulators.

Answer Summary

Correct answer: (1) Aspartic acid

---