Poster: Temperature Responses

Abs # 178: CYP90A2, involved in the brassinosteroid biosynthesis, has an effect on the chilling response of mungbean seedlings

Presenter:	Huang, Bin , huangbinntu@yahoo.com.tw
Authors	Huang, Bin  (A)   Young, Miin-Tzong  (A)   Chen, Swu-Ling  (A)   Chen, Yih-Ming  (A) (B)
Affiliations:	(A): Department of Botany, National Taiwan University (B): Center For Biotechnology, National Taiwan University

Low temperature is one of the important environmental stresses affecting plant growth and development in the tropical zone. The CYP90A2 gene, a new member of the cytochrome P450 super family, has been cloned by differential screening from a cDNA library of mungbean seedlings under chilling treatments, and its putative primary sequence shows 77% identity with Arabidopsis CPD/CYP90A1, which functions as a C-23 steroid hydroxylase. The CYP90A2 transcripts was not affected by the plant growth regulators, such as auxin, gibberellin, cytokinin, and abscisic acid, but was down-regulated by brassinolide, the biologically most active brassinosteroid. Thus the CYP90A2 protein may control a rate-limiting step in the biosynthesis of brassinosteroids in this species, with a similar function to the CPD/CYP90A1 gene in Arabidopsis. Both CYP90A2 mRNA and protein expression were decreased under the chilling condition and nuclear run-off assay also indicated that the expression of this gene was inhibited in the transcriptional level. The inhibition of growth of mungbean seedlings under chilling stress can be effectively relieved by the addition of small amount, nano to micro molar levels, of brassinolide. These results suggested that brassinolide has a great effect on the growth of mungbean seedlings under chilling stresses and the expression of the CYP90A2 gene seems to play an important role in the process of chilling responses.