生长素与脱落酸通过氧化还原调控植物根尖干细胞维持和分化的分子机制

The stem cell niche is localized in the root apical meristem that can differentiate into diversified cell types in roots. The differentiation rate of stem cells has a direct impact on the activity of the root meristem and thus determines developmental plasticity of the plant root system. Phytohormone auxin has been found to promote differentiation of stem cells, while abscisic acid (ABA) suppresses stem cell differentiation in Arabidopsis root meristems. However, the detailed molecular mechanism underlying the possible influence of these phytohormomes on root stem cell activity and thus subsequent modulation on root architecture remains elusive. Currently, we have screened several mutants named abo (ABA overly-sensitive) showing hypersensitivity to ABA in primary root growth by forward genetics. Interestingly, one of the mutants abo8 has short root and strongly reduced rates of stem cell differentiation, which are auxin-associated phenotypes. ABO8 encodes a pentatricopeptide repeat (PPR) protein that is localized to mitochondria and mutant abo8 accumulates more ROS (reactive oxygen species) than the wild type in the root tip. Exogenous applications of a reducing chemical glutathione (GSH) restored normal stem cell differentiation in abo8 root tip. It's known that redox homeostasis is involved in ABA-regulated plant growth and development and also related with auxin transport. Therefore, based on the gene function of ABO8, we will further systematically study the molecular mechanism underlying the cross-talk between Auxin and ABA regulating maintenance and differentiation of stem cells in the root meristem through effects on redox homeostasis. Our research may provide new genetic basis for crop high production and adversity-resistance breeding based on the targeted engineering of the root architecture.

植物根尖干细胞是植物根系发育可塑性的核心。生长素能够促进根尖干细胞的分化，脱落酸则可以抑制干细胞的分化。但是，这些激素通过怎样的互作模式来影响根尖干细胞微环境的稳态，目前尚不明确。我们通过正向遗传学的方法获得了一些在幼苗初生根阶段对脱落酸敏感的突变体abo (ABA overly-sensitive)，其中abo8主根短小，根尖干细胞的分化被抑制，这些表型缺陷可能与生长素功能紊乱有关。ABO8是定位在线粒体上的PPR蛋白，abo8根尖的ROS含量明显高于野生型，而外源施加还原性物质GSH降低根尖ROS水平可以恢复干细胞的正常分化。已知氧化还原参与了脱落酸调节植物生长发育的许多方面，并且与生长素的运输密切相关。因此，我们将以ABO8作为一个切入点，深入研究生长素与脱落酸通过氧化还原调控植物根尖干细胞维持和分化的分子生物学机制。期望本研究能为基于根型改良的作物高产抗逆育种提供新的理论依据。