Funtional analysis of MKK7-MPKs in plant development 
 Weiyan Jia, Baohua Li, Shujia Li, Yonghong Wang and Jiayang Li*

State Key Laboratory of Plant Genomics and National Center for Plant Gene Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China.
*Corresponding Author：Tel: (+8610) 6480 6577; Fax: (+8610) 6480 6595; E-mail: jyli@genetics.ac.cn

Abstract
Mitogen-activated protein kinase (MAPK) cascades play an important role in transducing environmental and developmental signals into adaptive and programmed responses. In higher plant, MAPK cascades are involved in a broad spectrum of signals, which include biotic and abiotic stresses, and hormone-mediated development. Our previous study have characterized a semidominant Arabidopsis thaliana bushy and dwarf1 (bud1) mutant. Molecular genetic analysis indicated that the bud1 phenotype is a result of increased expression of Arabidopsis MAPKINASE KINASE7 (MKK7), a member of plant mitogen-activated protein kinase kinase group D. We showed that BUD1/MKK7 is a functional kinase that affects plant architecture and negatively regulates polar auxin transport.
The Arabidopsis genome encodes a large number of MAPK signaling components, with more than 60 members of MAPKKK, 10 members of MKK and 20 members of MAPK. The mismatch between the numbers of MKKs and their putative MPK substrates suggests that individual MKKs should have the capacity to active more than one MPK. To elucidate the specificity of BUD1/MKK7 and its downstream MPKs in plant development, we first systemically screened the downstream substrates of MKK7 in vitro. Further, we characterized the function of BUD1/MKK7-MPKs in planta. Our study will provide evidence to explain how BUD1/MKK7 acts multiple roles in plant development.

Key words: MKK7, MPK, bud1, plant architecture, Arabidopsis thaliana