[原生質絲] 會因滲透壓改變而座落於原生質絲上的受器。20191029 Plant Physiology

Plasmodesmata
Oct 28, 2019
3 min read

Plasma Membrane-Associated Receptor-like Kinases Relocalize to Plasmodesmata in Response to Osmotic Stress

Magali S. Grison, Philip Kirk, Marie L. Brault, Xu Na Wu, Waltraud X. Schulze, Yoselin Benitez-Alfonso, Françoise Immel, and Emmanuelle M. Bayer

Abstract

Plasmodesmata act as key elements in intercellular communication, coordinating processes related to plant growth, development, and responses to environmental stresses. While many of the developmental, biotic, and abiotic signals are primarily perceived at the plasma membrane (PM) by receptor proteins, plasmodesmata also cluster receptor-like activities; whether these two pathways interact is currently unknown. Here, we show that specific PM-located Leu-rich-repeat receptor-like-kinases, Qian Shou kinase (QSK1) and inflorescence meristem kinase, which under optimal growth conditions are absent from plasmodesmata, rapidly relocate and cluster to the pores in response to osmotic stress. This process is remarkably fast, is not a general feature of PM-associated proteins, and is independent of sterol and sphingolipid membrane composition. Focusing on QSK1, previously reported to be involved in stress responses, we show that relocalization in response to mannitol depends on QSK1 phosphorylation. Loss-of-function mutation in QSK1 results in delayed lateral root (LR) development, and the mutant is affected in the root response to mannitol stress. Callose mediated plasmodesmata regulation is known to regulate LR development. We found that callose levels are reduced in the qsk1 mutant background with a root phenotype resembling ectopic expression of PdBG1, an enzyme that degrades callose at the pores. Both the LR and callose phenotypes can be complemented by expression of wild-type and phosphomimic QSK1 variants, but not by phosphodead QSK1 mutant, which fails to relocalize at plasmodesmata. Together, the data indicate that reorganization of receptor-like-kinases to plasmodesmata is important for the regulation of callose and LR development as part of the plant response to osmotic stress.

位於細胞膜周圍的受體激脢，會對滲透壓壓力作出反應而移動到原生質絲

摘要

原生質絲在調節各種植物生長、發育以及應對外界環境壓力的過程中，細胞溝通的環節裡，扮演了主要的角色。雖然許多主要的生長、生物性以及非生物性的訊息都由細胞膜上的受器蛋白來接收，但是原生質絲上也群聚了類似受器的反應。然而這兩個路徑是否有互相調節影響，目前仍然未知。在此，我們展示了一個位在細胞膜上，特別的富含白氨酸的類受器激脢 - 拳手激酶（QSK1）以及花芽分生組織激脢，這兩個蛋白質在良好的生長條件下，並不會座落於原生質絲上。在滲透壓改變的情況下，這兩個蛋白質會快速的反應，移動並且集中到原生質絲。這個過程相當的快速，不像一個普通位在細胞膜周圍蛋白質的行為。這個移動與膽固醇以及鞘脂的細胞膜成分並無關聯。QSK1在之前的研究中曾經報導會參與在壓力反應的過程中，我們也發現了，在甘露醇的處理下，這個位置的轉移是和QSK1的磷酸化相關。失去QSK1功能的突變植物會延遲側根的發育，而突變植物的根對於甘露醇壓力的反應也受到影響。已知經癒創葡聚醣調節原生質絲的機制會調節側根的生長。我們發現，在qsk1突變株中，癒創葡聚醣的量有降低，突變株也有與異位表現可分解癒創葡聚醣的酵素 - PdBG1植物有相似的外表型態。側跟以及癒創葡聚醣在突變植物中的影響，都可以藉由表現野生型的，或是模仿具有磷酸化的QSK1蛋白質來挽回，但是無法被磷酸化的QSK1，不但不會移動到原生質絲上，也不能補足這個功能性的缺失。總結而言，這些結果顯示，類受器激酶移動到原生質絲上的調控對於癒創葡聚醣、側跟發育以及對滲透壓改變的反應機制而言，非常的重要。