BAK7 displays unequal genetic redundancy with BAK1 in brassinosteroid signaling and early senescence in Arabidopsis.
BRI1-Associated kinase 1 (BAK1), a five leucine-rich-repeat containing receptor-like serine/threonine kinase, has been shown to have dual functions: mediating brassinosteroid (BR) signaling and acting in the BR-independent plant defense response. Sequence analysis has revealed that BAK1 has two homologs, BAK7 and BAK8. Because BAK8 deviates from the canonical RD kinase motif, we focused on the functional analysis of BAK7. The expression pattern and tissues in which BAK7 appeared partially overlapped with those observed for BAK1. Expression levels of BAK7 increased in the bak1 mutant. Overexpression of BAK7 rescued the bri1 mutant phenotype, indicating that BAK7 can compensate for BAK1 in BR-mediated processes, especially in the absence of BAK1. However, root and hypocotyl elongation patterns of transgenic plants overexpressing BAK1 or BAK7 appeared to be different from the patterns observed in a BRI1 overexpressor. Furthermore, the sensitivity of transgenic plants overexpressing BAK7 to brassinazole, a biosynthetic inhibitor of brassinolide (BL), did not change compared to that of wild-type plants. In addition, we generated transgenic plants expressing BAK7 RNA interference constructs and found severe growth retardation and early senescence in these lines. Taken together, these results suggest that BAK7 is a component of the BR signaling pathway, with varying degrees of genetic redundancy with BAK1, and that it affects plant growth via BL-independent pathways in vivo.
Jeong
Yu Jeong
YJ
Division of Biological Science, Sookmyung Women's University, Seoul, 140-742, Korea.
Shang
Yun
Y
Kim
Beg Hab
BH
Kim
Sun Young
SY
Song
Jae Hyo
JH
Lee
June Seung
JS
Lee
Myeong Min
MM
Li
Jianming
J
Nam
Kyoung Hee
KH
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology*; D015536:Down-Regulation; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D006914:Hydroxysteroids / Q000378:metabolism*; D018546:Hypocotyl / Q000254:growth & development; D008969:Molecular Sequence Data; D005810:Multigene Family; D009928:Organ Specificity; D010641:Phenotype; D010937:Plant Growth Regulators / Q000502:physiology*; D018517:Plant Roots / Q000254:growth & development; D030821:Plants, Genetically Modified; D011494:Protein Kinases / Q000172:deficiency / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017385:Sequence Homology; D015398:Signal Transduction / Q000502:physiology*
D029681:Arabidopsis Proteins; D006914:Hydroxysteroids; D010937:Plant Growth Regulators; D011993:Recombinant Fusion Proteins; D011494:Protein Kinases; C463660:BAK1 protein, Arabidopsis; C108270:BRI1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases