探討阿拉伯芥缺磷反應之可預啟性與磷酸鹽濃度對熱逆境記憶的影響

Primability of phosphorus starvation responses and the impact of phosphate concentrations on thermal memory

蘇子芸(Tzu-Yun Su)

指導教授 ： 邱子珍

國立臺灣大學/生物資源暨農學院/生物科技研究所/碩士(2022年)

https://doi.org/10.6342/NTU202201684

摘要

植物不可自由移動，其無法如同動物般依靠移動的方式來避免威脅，因此植物經常面臨環境逆境，例如：熱、乾旱以及營養缺失。若先前經歷逆境之經驗可使植物對於後續逆境產生不同反應，表示植物可被逆境預啟 (prime)，並藉此獲得逆境記憶。近年來，許多研究顯示植物具有對於熱、乾旱以及低溫之逆境記憶。然而，對於植物是否可被營養缺失逆境預啟或是養分是否影響其它環境逆境記憶的研究甚少，因此本實驗對此進行研究，主要目的有兩個：1) 探討阿拉伯芥對於缺磷逆境是否具有可預啟性 (primability)；2) 缺磷逆境是否影響阿拉伯芥的熱逆境記憶。第一個實驗藉由比較缺磷誘導基因之表現量判斷植物是否具有缺磷預啟性；第二個實驗利用分析熱誘導基因在生長於不同濃度營養成分之培養基之植物的表現量，推測營養成分是否影響熱記憶。
在第一個實驗中，我們藉由分析6個參與磷信號傳遞、磷轉運蛋白以及脂質重塑之缺磷誘導基因的表現，發現缺磷逆境的預啟不會影響觸發 (triggering) 後這6個基因的表現，說明在我們的試驗條件下，所分析之阿拉伯芥缺磷誘導基因對於缺磷逆境不具有可預啟性。在植物補給磷後，少數缺磷逆境基因，例如：induced by phosphate starvation 1 (IPS1) 和induced by phosphate starvation 2 (At4)，雖然表現下降，但仍維持某程度的反應狀態，顯示阿拉伯芥具有缺磷逆境之轉錄記憶，使基因在逆境消失後，依舊保持反應狀態。RNA定序發現經本實驗之處理後，阿拉伯芥具有兩種類型的缺磷逆境之轉錄記憶，且分析不同基因Gene Ontology (GO) 之biological process功能性註解得知，rapid response genes、type I transcript memory genes以及type III transcript memory genes也參與其它環境逆境之反應，因此推測缺磷逆境與其它環境逆境間可能具有相互作用。在第二個實驗中，我們將植物培養於不同磷濃度與不同營養成分濃度的Hoagland營養液，並分析熱誘導基因之表現量，例如：heat shock transcription factor A1E (HSFA1E) 和ascorbate peroxidase 2 (APX2)。結果顯示，改變Hoagland營養液中的磷濃度或總營養成分濃度會對熱記憶產生影響，且低磷環境可以增強部分植物熱逆境誘導基因的表現量。
綜上所述，在本次實驗的試驗條件下發現，針對所分析之缺磷誘導基因的表現結果顯示，阿拉伯芥對於缺磷逆境不具有可預啟性，但其對於缺磷逆境具有記憶，以及低磷環境可以增強熱誘導基因的表現量，具有提升阿拉伯芥熱逆境反應預啟性的傾向。

關鍵字

阿拉伯芥 ； 缺磷逆境 ； 可預啟性 ； 逆境記憶 ； 熱記憶

並列摘要

Plants are immobile and frequently undergo various abiotic stresses, such as heat, dehydration, and nutrient deficiency. Pre-exposure to stress can make plants respond differently to subsequent stress, suggesting that plants can be primed with the ability to memorize the prior experience of stress. Recent studies showed plants possess stress memory of heat, dehydration and cold; however, there is less-understanding of plant nutrient stress primability, and the coordination of nutrient status and other stress memory. Here, we asked 1) whether Arabidopsis has primability of phosphate (Pi) starvation; 2) whether nutrient accessibility affects the thermal memory of Arabidopsis.
In the first experiment, we compared the expression of several Pi starvation-induced (PSI) genes between the seedlings with or without priming to assess the primability of Pi starvation. We found that priming of low Pi did not affect the expression of six PSI genes involved in Pi signaling, Pi transport or lipid remodeling after triggering. There results indicated that six PSI genes we tested possessed no primablity of Pi starvation under our conditions. However, the expression level of a small subset of PSI genes, such as induced by phosphate starvation 1 (IPS1) and induced by phosphate starvation 2 (At4) , remained upregulated even after Pi replenishment. This result indicated that Arabidopsis possesses the transcript memory of Pi starvation to sustain the upregulation during the stress-free phase. RNA sequencing analysis showed Arabidopsis might have two types of transcript memory patterns of Pi starvation. The biological process Gene Ontology (GO) terms of non-memory and memory genes were enriched in the responses to several other stresses, suggesting that the crosstalk of Pi starvation with other stresses.
In the second experiment, we compared the expression of heat-induced genes in the seedlings grown on media with different Hoagland nutrient concentrations to evaluate the impact of nutrients on thermal memory. Based on the expression of heat-induced memory genes, such as heat shock transcription factor A1E (HSFA1E), ascorbate peroxidase 2 (APX2), we found the change of Pi or the supply of nutrient could affect in thermal memory. Noteworthily, low Pi media enhanced the expression of several heat-induced memory genes.
In summary, this study suggested that Arabidopsis possesses no primability of Pi starvation based on the expression of selected PSI genes under the conditions tested. However, there are several genes belonging to transcript memory genes of Pi starvation, and low Pi conditions may force the primability of thermal memory.

並列關鍵字

Arabidopsis thaliana ； phosphate (Pi) starvation ； primability ； stress memory ； thermal memory

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