OPEN ACCESS ARTICLE

This Article Free via Open Access: OA OA Full Text Full Text (PDF) Supplemental Data OA All Versions of this Article: 151/3/1377    most recent pp.109.143685v2 pp.109.143685v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Google Scholar Articles by Lee, H. W. Articles by Kim, J. PubMed PubMed Citation Articles by Lee, H. W. Articles by Kim, J. Agricola Articles by Lee, H. W. Articles by Kim, J.

DEVELOPMENT AND HORMONE ACTION

LBD18/ASL20 Regulates Lateral Root Formation in Combination with LBD16/ASL18 Downstream of ARF7 and ARF19 in Arabidopsis^{1,[C],[W],[OA]}

Department of Plant Biotechnology and Agricultural Plant Stress Research Center, Chonnam National University, Buk-Gu, Gwangju 500–757, Korea

The LATERAL ORGAN BOUNDARIES DOMAIN/ASYMMETRIC LEAVES2-LIKE (LBD/ASL) genes encode proteins harboring a conserved amino acid domain, referred to as the LOB (for lateral organ boundaries) domain. While recent studies have revealed developmental functions of some LBD genes in Arabidopsis (Arabidopsis thaliana) and in crop plants, the biological functions of many other LBD genes remain to be determined. In this study, we have demonstrated that the lbd18 mutant evidenced a reduced number of lateral roots and that lbd16 lbd18 double mutants exhibited a dramatic reduction in the number of lateral roots compared with lbd16 or lbd18. Consistent with this observation, significant β-glucuronidase (GUS) expression in Pro_LBD18:GUS seedlings was detected in lateral root primordia as well as in the emerged lateral roots. Whereas the numbers of primordia of lbd16, lbd18, and lbd16 lbd18 mutants were similar to those observed in the wild type, the numbers of emerged lateral roots of lbd16 and lbd18 single mutants were reduced significantly. lbd16 lbd18 double mutants exhibited additively reduced numbers of emerged lateral roots compared with single mutants. This finding indicates that LBD16 and LBD18 may function in the initiation and emergence of lateral root formation via a different pathway. LBD18 was shown to be localized into the nucleus. We determined whether LBD18 functions in the nucleus using a steroid regulator-inducible system in which the nuclear translocation of LBD18 can be regulated by dexamethasone in the wild-type, lbd18, and lbd16 lbd18 backgrounds. Whereas LBD18 overexpression in the wild-type background induced lateral root formation to some degree, other lines manifested the growth-inhibition phenotype. However, LBD18 overexpression rescued lateral root formation in lbd18 and lbd16 lbd18 mutants without inducing any other phenotypes. Furthermore, we demonstrated that LBD18 overexpression can stimulate lateral root formation in auxin response factor7/19 (arf7 arf19) mutants with blocked lateral root formation. Taken together, our results suggest that LBD18 functions in the initiation and emergence of lateral roots, in conjunction with LBD16, downstream of ARF7 and ARF19.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jungmook Kim (jungmkim{at}chonnam.ac.kr).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.143685

^* Corresponding author; e-mail jungmkim{at}chonnam.ac.kr.

Received June 25, 2009; accepted August 25, 2009; published August 28, 2009.