The involvement of small auxin-up RNA proteins (SAURs) in leaf senescence has been more and more acknowledged, but the detailed mechanisms remain unclear. In the present study, we performed yeast two-hybrid assays (Y2Hs) and identified SAUR49 as an interactor of SSPP, which is a PP2C protein phosphatase that negatively regulates Arabidopsis leaf senescence by suppressing the leucine-rich repeat receptor-like protein kinase (LRR-RLK) SARK, as reported previously by our group. The interaction between SAUR49 and SSPP was further confirmed in planta. Functional characterization revealed that SAUR49 is a positive regulator of leaf senescence. The accumulation level of SAUR49 protein increased during natural leaf senescence in Arabidopsis. The transcript level of SAUR49 was upregulated during SARK-induced premature leaf senescence but downregulated during SSPP-mediated delayed leaf senescence. Overexpression of SAUR49 significantly accelerated both natural and dark-induced leaf senescence in Arabidopsis. More importantly, SAUR49 overexpression completely reversed SSPP-induced delayed leaf senescence. In addition, overexpression of SAUR49 reversed the decreased plasma membrane (PM) H+-ATPase activity mediated by SSPP. Taken together, the results showed that SAUR49 functions in accelerating the leaf senescence process via the activation of SARK-mediated leaf senescence signalling by suppressing SSPP. We further identified four other SSPP-interacting SAURs, SAUR30, SAUR39, SAUR41 and SAUR72, that may act redundantly with SAUR49 in regulating leaf senescence. All these observations indicated that certain members of the SAUR family may serve as an important hub that integrates various hormonal and environmental signals with senescence signals in Arabidopsis.

中文翻译：

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SAUR49 可以通过抑制拟南芥中的 SSPP 来积极调节叶片衰老。

植物生长素小分子 RNA 蛋白 (SAUR) 在叶片衰老中的作用越来越得到认可，但具体机制仍不清楚。在本研究中，我们进行了酵母双杂交试验 (Y2Hs) 并确定 SAUR49 作为 SSPP 的相互作用物，SSPP 是一种 PP2C 蛋白磷酸酶，通过抑制富含亮氨酸的重复受体样蛋白激酶 (LRR) 来负调节拟南芥叶片衰老。 -RLK) SARK，正如我们小组先前报道的那样。SAUR49 和 SSPP 之间的相互作用在植物中得到进一步证实。功能表征表明 SAUR49 是叶片衰老的正调节因子。SAUR49 蛋白的积累水平在拟南芥自然叶片衰老过程中增加。SAUR49 的转录水平在 SARK 诱导的叶片过早衰老过程中上调，但在 SSPP 介导的叶片延迟衰老过程中下调。SAUR49 的过表达显着加速了拟南芥中自然和黑暗诱导的叶片衰老。更重要的是，SAUR49 过表达完全逆转了 SSPP 诱导的延迟叶片衰老。此外，SAUR49 的过表达逆转了由 SSPP 介导的质膜 (PM) H+-ATPase 活性降低。总之，结果表明 SAUR49 通过抑制 SSPP 激活 SARK 介导的叶片衰老信号，从而加速叶片衰老过程。我们进一步确定了其他四种与 SSPP 相互作用的 SAUR，SAUR30、SAUR39、SAUR41 和 SAUR72，它们可能与 SAUR49 在调节叶片衰老方面发挥冗余作用。