生长素反应因子6(ARF6)和ARF8促进赤霉素介导的下胚轴木质部扩张和形成层动态平衡

在次生生长过程中，维管形成层不断产生植物器官、木材(木质部)和韧皮部(韧皮部)的增厚。在拟南芥下胚轴和根中，我们可以根据细胞形态和产量来区分二次生长的两个阶段。第一阶段是木质部和韧皮部同样产生的阶段，在木质部扩展阶段之前，木质部形成增强，木质部纤维分化。

已知赤霉素(GA)通过降解Della蛋白来触发这一发育转变，形成层主控调控因子BREVIPEDICELLUS/Knat1(BP/Knat1)以及类似受体的激酶ERECTA和ERL1调节GA下游的这一过程。然而，我们对GA介导的次级生长背后的调控网络的理解仍然有限。在这里，我们证明Della介导的木质部扩展主要是通过RGA和GAI实现的，RGA和GAI促进形成层衰老。我们进一步证明，生长素反应因子(ARF6)和ARF8在木质部膨大阶段能特异性地抑制韧皮部增殖和诱导形成层衰老，它们与Dellas发生物理上的相互作用。

此外，ARF6和ARF8背景下BP的失活揭示了ARF6和ARF8在形成层建立和维持中的重要作用。总体而言，我们的研究结果阐明了GA和生长素在植物次生生长过程中的关键激素相互作用。

During secondary growth, the thickening of plant organs, wood (xylem) and bast (phloem) are continuously produced by the vascular cambium. In Arabidopsis hypocotyl and root, we can distinguish two phases of secondary growth based on cell morphology and production rate. The first phase, in which xylem and phloem are equally produced, precedes the xylem expansion phase in which xylem formation is enhanced and xylem fibers differentiate. It is known that Gibberellins (GA) trigger this developmental transition via the degradation of DELLA proteins and that the cambium master regulator BREVIPEDICELLUS/KNAT1 (BP/KNAT1) and the receptor like kinases ERECTA and ERL1 regulate this process downstream of GA. However, our understandings on the regulatory network underlying GA-mediated secondary growth, are still limited. Here, we demonstrate that DELLA-mediated xylem expansion is mainly achieved through RGA and GAI and that RGA and GAI promote cambium senescence. We further show that AUXIN RESPONSE FACTOR (ARF6) and ARF8, which physically interact with DELLAs, specifically repress phloem proliferation and induce cambium senescence during the xylem expansion phase. Moreover, the inactivation of BP in arf6 arf8 background revealed an essential role for ARF6 and ARF8 in cambium establishment and maintenance. Overall, our results shed light on a pivotal hormone cross-talk between GA and auxin in the context of plant secondary growth.

https://www.biorxiv.org/content/10.1101/2020.11.13.381558v1?rss=1

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