Department of Biology, Chungbuk National University, Cheongju, 28644, Republic of Korea.
National Agrobiodiversity Center, National Academy of Agricultural Science RDA, Jeonju, 54875, Republic of Korea.
Planta. 2019 May;249(5):1391-1403. doi: 10.1007/s00425-019-03094-6. Epub 2019 Jan 23.
BR signaling pathways facilitate xylem differentiation and wood formation by fine tuning SlBZR1/SlBZR2-mediated gene expression networks involved in plant secondary growth. Brassinosteroid (BR) signaling and BR crosstalk with diverse signaling cues are involved in the pleiotropic regulation of plant growth and development. Recent studies reported the critical roles of BR biosynthesis and signaling in vascular bundle development and plant secondary growth; however, the molecular bases of these roles are unclear. Here, we performed comparative physiological and anatomical analyses of shoot morphological growth in a cultivated wild-type tomato (Solanum lycopersicum cv. BGA) and a BR biosynthetic mutant [Micro Tom (MT)]. We observed that the canonical BR signaling pathway was essential for xylem differentiation and sequential wood formation by facilitating plant secondary growth. The gradual retardation of xylem development phenotypes during shoot vegetative growth in the BR-deficient MT tomato mutant recovered completely in response to exogenous BR treatment or genetic complementation of the BR biosynthetic DWARF (D) gene. By contrast, overexpression of the tomato Glycogen synthase kinase 3 (SlGSK3) or CRISPR-Cas9 (CR)-mediated knockout of the tomato Brassinosteroid-insensitive 1 (SlBRI1) impaired BR signaling and resulted in severely defective xylem differentiation and secondary growth. Genetic modulation of the transcriptional activity of the tomato Brassinazole-resistant 1/2 (SlBZR1/SlBZR2) confirmed the positive roles of BR signaling pathways for xylem differentiation and secondary growth. Our data indicate that BR signaling pathways directly promote xylem differentiation and wood formation by canonical BR-activated SlBZR1/SlBZR2.
BR 信号通路通过精细调节 SlBZR1/SlBZR2 介导的植物次生生长相关基因表达网络，促进木质部分化和木材形成。油菜素内酯（BR）信号转导及其与多种信号线索的交叉对话参与了植物生长和发育的多效调节。最近的研究报道了 BR 生物合成和信号转导在维管束发育和植物次生生长中的关键作用；然而，这些作用的分子基础尚不清楚。在这里，我们对栽培野生型番茄（Solanum lycopersicum cv. BGA）和 BR 生物合成突变体[Micro Tom（MT）]的芽形态生长进行了比较生理和解剖分析。我们观察到，BR 信号通路在木质部分化和顺序木材形成中起关键作用，促进植物次生生长。BR 缺陷型 MT 番茄突变体在芽营养生长过程中木质部发育表型逐渐滞后，对外源 BR 处理或 BR 生物合成 DWARF（D）基因的遗传互补完全恢复。相比之下，番茄 Glycogen synthase kinase 3（SlGSK3）的过表达或 CRISPR-Cas9（CR）介导的番茄 Brassinosteroid-insensitive 1（SlBRI1）的敲除破坏了 BR 信号转导，导致木质部分化和次生生长严重缺陷。番茄 Brassinazole-resistant 1/2（SlBZR1/SlBZR2）转录活性的遗传调节证实了 BR 信号通路对木质部分化和次生生长的积极作用。我们的数据表明，BR 信号通路通过激活 SlBZR1/SlBZR2 直接促进木质部分化和木材形成。
