Department of Plant Biotechnology and Agricultural Plant Stress Research Center, Chonnam National University, Buk-Gu, Gwangju 500-757, Korea.
Plant Physiol. 2009 Nov;151(3):1377-89. doi: 10.1104/pp.109.143685. Epub 2009 Aug 28.
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 beta-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.
LATERAL ORGAN BOUNDARIES DOMAIN/ASYMMETRIC LEAVES2-LIKE (LBD/ASL) 基因编码具有保守氨基酸结构域的蛋白质，该结构域被称为 LOB（ lateral organ boundaries，侧生器官边界）结构域。尽管最近的研究揭示了一些 LBD 基因在拟南芥（Arabidopsis thaliana）和作物植物中的发育功能，但许多其他 LBD 基因的生物学功能仍有待确定。在这项研究中，我们证明了 lbd18 突变体的侧根数量减少，并且 lbd16 lbd18 双突变体的侧根数量与 lbd16 或 lbd18 相比显著减少。与这一观察结果一致，Pro(LBD18):GUS 幼苗中的β-葡萄糖醛酸酶（GUS）表达在侧根原基以及出现的侧根中显著检测到。尽管 lbd16、lbd18 和 lbd16 lbd18 突变体的原基数量与野生型观察到的数量相似，但 lbd16 和 lbd18 单突变体的出现的侧根数量显著减少。lbd16 lbd18 双突变体的出现侧根数量比单突变体减少。这一发现表明，LBD16 和 LBD18 可能通过不同的途径在侧根形成的起始和出现中发挥作用。LBD18 被证明定位于细胞核内。我们使用类固醇调节剂诱导系统确定 LBD18 是否在核内发挥作用，在该系统中，野生型、lbd18 和 lbd16 lbd18 背景下，LBD18 的核易位可由地塞米松调节。虽然 LBD18 在野生型背景下的过表达在某种程度上诱导了侧根的形成，但其他品系表现出生长抑制表型。然而，LBD18 过表达在 lbd18 和 lbd16 lbd18 突变体中挽救了侧根的形成，而没有诱导任何其他表型。此外，我们证明 LBD18 过表达可以刺激 auxin response factor7/19（arf7 arf19）突变体中侧根的形成，这些突变体的侧根形成受阻。总之，我们的结果表明，LBD18 与 LBD16 一起，在 ARF7 和 ARF19 下游，在侧根的起始和出现中发挥作用。
