Moubayidin Laila, Salvi Elena, Giustini Leonardo, Terpstra Inez, Heidstra Renze, Costantino Paolo, Sabatini Sabrina
Laboratory of Functional Genomics and Proteomics of Model Systems, Dipartimento di Biologia e Biotecnologie, Università La Sapienza, P.le Aldo Moro, 5, 00185, Rome, Italy.
Crop Genetics Department, John Innes Centre, Norwich Research Park, Norwich, NR4 7UH, UK.
Planta. 2016 May;243(5):1159-68. doi: 10.1007/s00425-016-2471-0. Epub 2016 Feb 5.
SCARECROW controls Arabidopsis root meristem size from the root endodermis tissue by regulating the DELLA protein RGA that in turn mediates the regulation of ARR1 levels at the transition zone. Coherent organ growth requires a fine balance between cell division and cell differentiation. Intriguingly, plants continuously develop organs post-embryonically thanks to the activity of meristems that allow growth and environmental plasticity. In Arabidopsis thaliana, continued root growth is assured when division of the distal stem cell and their daughters is balanced with cell differentiation at the meristematic transition zone (TZ). We have previously shown that at the TZ, the cytokinin-dependent transcription factor ARR1 controls the rate of differentiation commitment of meristematic cells and that its activities are coordinated with those of the distal stem cells by the gene SCARECROW (SCR). In the stem cell organizer (the quiescent center, QC), SCR directly suppresses ARR1 both sustaining stem cell activities and titrating non-autonomously the ARR1 transcript levels at the TZ via auxin. Here, we show that SCR also exerts a fine control on ARR1 levels at the TZ from the endodermis by sustaining gibberellin signals. From the endodermis, SCR controls the RGA REPRESSOR OF ga1-3 (RGA) DELLA protein stability throughout the root meristem, thus controlling ARR1 transcriptional activation at the TZ. This guarantees robustness and fineness to the control of ARR1 levels necessary to balance cell division to cell differentiation in sustaining coherent root growth. Therefore, this work advances the state of the art in the field of root meristem development by integrating the activity of three hormones, auxin, gibberellin, and cytokinin, under the control of different tissue-specific activities of a single root key regulator, SCR.
稻草人（SCARECROW）通过调控DELLA蛋白RGA来控制拟南芥根分生组织的大小，而RGA反过来又介导了过渡区ARR1水平的调控。协调的器官生长需要细胞分裂和细胞分化之间的精细平衡。有趣的是，由于分生组织的活性，植物在胚胎后阶段能够持续发育器官，这种活性允许生长和环境可塑性。在拟南芥中，当远端干细胞及其子代的分裂与分生组织过渡区（TZ）的细胞分化达到平衡时，根的持续生长就能得到保证。我们之前已经表明，在TZ区，细胞分裂素依赖性转录因子ARR1控制着分生组织细胞的分化速率，并且其活性通过稻草人（SCR）基因与远端干细胞的活性相协调。在干细胞组织中心（静止中心，QC），SCR直接抑制ARR1，既维持干细胞活性，又通过生长素非自主地调节TZ区的ARR1转录水平。在这里，我们表明SCR还通过维持赤霉素信号，从内皮层对TZ区的ARR1水平进行精细调控。在内皮层，SCR控制着整个根分生组织中ga1-3的RGA阻遏物（RGA）DELLA蛋白的稳定性，从而控制TZ区ARR1的转录激活。这确保了在维持根的连贯生长过程中，平衡细胞分裂与细胞分化所需的ARR1水平调控的稳健性和精确性。因此，这项工作通过整合生长素、赤霉素和细胞分裂素这三种激素的活性，在单个根关键调节因子SCR的不同组织特异性活性控制下，推动了根分生组织发育领域的技术水平。
