Light and gravity are two key environmental factors that control plant growth and architecture. However, the molecular basis of the coordination of light and gravity signaling in plants remains obscure. Here, we report that two classes of transcription factors, PHYTOCHROME INTERACTING FACTORS (PIFs) and ELONGATED HYPOCOTYL5 (HY5), can directly bind and activate the expression of LAZY4, a positive regulator of gravitropism in both shoots and roots in Arabidopsis. In hypocotyls, light promotes degradation of PIFs to reduce LAZY4 expression, which inhibits the negative gravitropism of hypocotyls. LAZY4 overexpression can partially rescue the negative gravitropic phenotype of pifq in the dark without affecting amyloplast development. Our identification of the PIFs-LAZY4 regulatory module suggests the presence of another role for PIF proteins in gravitropism, in addition to a previous report demonstrating that PIFs positively regulate amyloplast development to promote negative gravitropism in hypocotyls. In roots, light promotes accumulation of HY5 proteins to activate expression of LAZY4, which promotes positive gravitropism in roots. Together, our data indicate that light exerts opposite regulation of LAZY4 expression in shoots and roots by mediating the protein levels of PIFs and HY5, respectively, to inhibit the negative gravitropism of shoots and promote positive gravitropism of roots in Arabidopsis.

光线和重力是控制植物生长和结构的两个关键环境因素。然而，植物中光和重力信号的协调作用的分子基础仍然不清楚。在这里，我们报道了两类转录因子，植物染色体相互作用因子（PIF）和长粒HYPOCOTYL5（HY5），可以直接结合并激活LAZY4的表达，LAZY4是拟南芥中茎和根中引力的正向调节剂。在下胚轴中，光会促进PIF降解，从而降低LAZY4表达，从而抑制下胚轴的负重力。LAZY4过表达可以部分挽救pifq的负性趋性表型在黑暗中不影响淀粉体的发育。我们对PIFs- LAZY4调节模块的鉴定表明，PIF蛋白在重力趋向性中还存在另一种作用，除了先前的报告表明PIF积极调节淀粉状体的发育以促进下胚轴的负向向性。在根中，光促进HY5蛋白的积累，从而激活LAZY4的表达，从而促进根中的正向重力作用。在一起，我们的数据表明光分别通过介导PIF和HY5的蛋白质​​水平对芽和根中的LAZY4表达产生相反的调节作用，从而抑制拟南芥中芽的负向着性并促进根的向着性。