Poster: Hormones

Abs # 571: The Arabidopsis axin rsponse fctor 8 (ARF8) is involved in light and auxin signal transduction

Presenter:	Tian, Chang-en , cetian@ees.hokudai.ac.jp
Authors	Tian, Chang-en  (A)   Muto,  Hideki  (A)   Matamura, Tomoyuki  (A)   Tatematsu, Kiyoshi  (A)   Yamamoto, Kotaro T.  (A)
Affiliations:	(A): Div. Biol. Sci., Grad. School of Environ. Earth Sci., Hokkaido University

ARFs have been shown to play a central role in multiple auxin-dependent phenomena. To comprehensively understand the role of ARFs in auxin action, we have been carrying out phenotypic characterization of loss-of-function mutants of ARF genes. Screening of T-DNA insertion lines of Arabidopsis by PCR, we have isolated a mutant line, arf8-1, in which T-DNA inserts into the third exon of ARF8 gene. arf8-1 seedlings showed the long-hypocotyl phenotype when grown in either white, red, far-red or blue light. Growth orientation of hypocotyl in wild type is randomized under red-light condition. However, arf8-1 hypocotyls grew upward in the same condition. These results indicate that light sensitivity is reduced in arf8-1. Mature arf8-1 plants displayed stronger apical dominance than wild type. Etiolated arf8-1 seedlings showed slightly reduced phototropism in hypocotyls, but their gravitropism was not affected significantly. Growth of both hypocotyls and roots was inhibited by IAA in arf8-1 as strongly as in wild type. These results suggest that sensitivity to auxin is also a little affected in arf8-1. Introduction of ARF8 ORF driven by ARF8 natural promoter into arf8-1 mutant restored the arf8-1 mutant phenotypes tested. Using ARF8 promoter::GUS, ARF8 gene was found to strongly express in hypocotyls of light-grown seedlings, but it expressed faintly in the dark. It also expressed constitutively in apical shoot and root meristems. All the above results suggest that ARF8 is involved in light and auxin signal transduction. Considering that shy2/iaa3 is a constitutively photomorphogenetic mutant, ARF and Aux/IAA family genes are likely to regulate a complex network integrating auxin and light signals.