Disease relevance of SERK1

• To determine the intrinsic biochemical properties of the AtSERK1 protein, we have expressed the intracellular catalytic domain as a glutathione S-transferase fusion protein in Escherichia coli [1].
• Ectopic expression of the full-length AtSERK1 cDNA under the control of the cauliflower mosaic virus 35S promoter did not result in any altered plant phenotype [2].

High impact information on SERK1

• These results suggest that KAPP is an integral part of the AtSERK1 endocytosis mechanism [3].
• AtSERK1(T463A)-CFP and AtSERK1(3T-->A)-CFP proteins were partially sequestered intracellularly in the absence of KAPP-YFP protein, suggesting an active role for KAPP dephosphorylation of threonine residues in the AtSERK1 A-loop in receptor internalization [3].
• Using mutant AtSERK1 proteins in which Thr 462, Thr 463, and Thr 468 in the A-loop of the AtSERK1 kinase domain were replaced by alanines, we show that phosphorylation status of the receptor is involved in interaction with KAPP [3].
• The AtSERK1 protein is a plasma membrane-located LRR receptor-like serine threonine kinase that is transiently expressed during plant embryogenesis [3].
• The SERK1 mutant allele serk1-1 enhances the phenotype of the weak BRI1 allele bri1-119 [4].

Biological context of SERK1

• Arabidopsis thaliana SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 (SERK1) is a leucine-rich repeat receptor-like kinase (LRR-RLK) involved in the acquisition of embryogenic competence and in male sporogenesis [4].
• Finally, the MADS box transcription factor AGAMOUS-LIKE15 and an uncharacterized zinc finger protein, a member of the CONSTANS family, were identified as part of the SERK1 complex [4].
• Fluorescent lifetime imaging microscopy (FLIM) was used to detect F??rster resonance energy transfer (FRET) between CrFP/YFP-tagged CDC48A and SERK1 [5].
• In young buds, double mutant anthers developed normally, but serk1 serk2 microsporangia produced more sporogenous cells that were unable to develop beyond meiosis [6].
• On the basis of this model, threonine residues in the AtSERK1 activation loop of catalytic subdomain VIII are potential targets for phosphorylation [1].

Anatomical context of SERK1

• CDC48A was found to interact only with SERK1 in small areas at the PM, but not in endosomes [5].
• The Arabidopsis thaliana SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) family of plasma membrane receptors consists of five closely related members [7].
• Replacing Thr-468 with either alanine or glutamic acid not only obliterated the ability of the AtSERK1 protein to be phosphorylated but also inhibited phosphorylation on myelin basic protein and casein, suggesting that Thr-468 is essential for AtSERK-mediated signaling [1].
• The AtSERK1 cDNA was fused to two different variants of green fluorescent protein (GFP), a yellow-emitting GFP (YFP) and a cyan-emitting GFP (CFP), and transiently expressed in both plant protoplasts and insect cells [8].
• CDC48A and somatic embryogenesis receptor like kinase 1 (SERK1) were found to co-localize in the endoplasmatic reticulum (ER) and at the plasma membrane (PM), but not in endosomal compartments [5].

Associations of SERK1 with chemical compounds

• The AtSERK1-glutathione S-transferase fusion protein mainly autophosphorylates on threonine residues (K(m) for ATP, 4 x 10(-6) m), and the reaction is Mg(2+) dependent and inhibited by Mn(2+) [1].
• AtSERK1 phosphorylation on myelin basic protein and casein showed tyrosine, serine, and threonine as targets, demonstrating that AtSERK1 is a dual specificity kinase [1].
• Elimination of the extracellular leucine zipper domain reduced the YFP/CFP emission ratio to control levels indicating that without the leucine zipper domain AtSERK1 is monomeric [8].
• Although the studies with M. truncatula indicate that somatic embryogenesis is associated with high SERK expression, auxin alone does not induce somatic embryogenesis as in carrot (Daucus carota) and Arabidopsis [9].

Physical interactions of SERK1

• These findings confirm and extend our previous findings that CDC48A in plants directly interacts with SERK1 [5].
• Our results show that AtSERK1 interacts with the kinase-associated protein phosphatase (KAPP) in vitro [3].

Enzymatic interactions of SERK1

• In vitro, the AtSERK1 kinase domain is able to transphosphorylate and bind both AtCDC48 and GF14lambda [10].

Other interactions of SERK1

• Both SERK1 and SERK2 are expressed widely in locules until stage 6 anthers and are more concentrated in the tapetal cell layer later [6].
• Collectively, these results suggest that apart from SERK3, SERK1 is also involved in the brassinolide signaling pathway [4].
• Further confocal microscopic and molecular analyses showed that serk1 serk2 double mutant anthers lack development of the tapetal cell layer, which accounts for the microspore abortion and male sterility [6].

Analytical, diagnostic and therapeutic context of SERK1

• We have cloned a SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK) gene from Medicago truncatula (MtSERK1) and examined its expression in culture using real time PCR [9].

References