Long-distance control of the scion by the rootstock under drought stress as revealed by transcriptome sequencing and mobile mRNA identification

研究背景：Grafting with pumpkin rootstock is commonly used not only to improve the quality of cucumber fruits but also to confer biotic or abiotic stress tolerance. 

植物嫁接不仅是提高果实品质和生物/非生物胁迫耐受性的重要手段，同样也能够有助于研究不同环境条件下调控因子转移特征和功能的解析。

科学问题：However, the molecular mechanism of the response of grafted cucumbers to drought stress and the possible roles of mobile mRNAs in improving stress tolerance have remained obscure. 研究内容：Hence, we conducted transcriptome sequencing and combined it with morphophysiological experiments to compare the response of homografts (cucumber as scion and rootstock) and heterografts (cucumber as scion and pumpkin as rootstock) to drought stress. 

然而，嫁接黄瓜对干旱胁迫反应的分子机制以及移动mRNAs在提高胁迫耐受性中的作用仍不清楚

结果1#： After applying drought stress, homografts and heterografts expressed 2960 and 3088 genes, respectively, in response to the stress. The differentially expressed genes identified in heterografts under drought stress were categorized into different stress-responsive groups, such as carbohydrate metabolism (involved in osmotic adjustment by sugar accumulation), lipid and cell wall metabolism (involved in cell membrane integrity by a reduction in lipid peroxidation), redox homeostasis (increased antioxidant enzyme activities), phytohormone (increased abscisic acid content), protein kinases, and transcription factors, using MapMan software. Earlier and greater H2O2 accumulation in xylem below the graft union was accompanied by leaf abscisic acid accumulation in heterografts in response to drought stress. 

在干旱胁迫下异种嫁接植物中鉴定出的差异表达基因（DEGs）可分为不同的响应组合，如碳水化合物代谢（通过糖积累参与渗透调节），脂质和细胞壁代谢（通过减少脂质过氧化参与细胞膜完整性），氧化还原稳态（增加抗氧化酶活性），植物激素（增加ABA含量），蛋白激酶和转录因子等。南瓜砧木通过控制对黄瓜接穗的叶片中ABA的提前积累来提高其抗干旱能力。另外，异体嫁接（南瓜-黄瓜）植株叶片比同体嫁接（黄瓜-黄瓜）植株更早感受到干旱胁迫，叶片中ABA积累更早，积累量更大。ABA作为一种关键的植物激素，可诱导异种嫁接植株的抗旱性改变，如有效的渗透调节、维持细胞膜的完整性、改善抗氧化系统和降低气孔导度（Gs）。

结果2#： Greater leaf abscisic acid helped heterografted cucumbers to sense and respond to drought stress earlier than homografts. The timely response of heterografts to drought stress led to the maintenance of higher water content in the leaves even in the late stage of drought stress. 

较高的叶片脱落酸有助于异种嫁接黄瓜比同种嫁接黄瓜更早地感知和响应干旱胁迫。异种嫁接对干旱胁迫的及时响应导致即使在干旱胁迫后期，叶片中的水分含量也保持较高。

结果3#： The mobile mRNAs identified in heterografts were mostly related to photosynthesis, which would be the possible reason for improved chlorophyll content and maximum photochemical efficiency of photosystem II (Fv/Fm). The existence of some stress-responsive pumpkin (rootstock) mRNAs in cucumber (scion), such as heat shock protein (HSP70, a well-known stress-responsive gene), led to higher proline accumulation than in homografts. 

除了在异种嫁接中早期感知和信号转导外，在胁迫条件下南瓜mRNA也可以通过砧-穗转移来提高黄瓜耐旱能力。该研究在黄瓜接穗中鉴定到多个与干旱胁迫耐受性相关的南瓜可移动mRNA（mobile mRNAs，mb-mRNAs），如HSP70等。相关报道表明HSP70可以通过增加脯氨酸含量来提高抗旱性。此外，富集分析表明，干旱条件下接穗中特异的mb-mRNAs可富集到光合作用相关的反应途径中，如光系统II、光反应、叶绿体膜和叶绿素等，这可能是异种嫁接植株光合作用增强的主要原因。

结论：Expression of mobile and immobile stress-responsive mRNAs and timely response of heterografts to drought stress could improve drought tolerance in pumpkin-rooted plants.

表达可移动和不可移动的胁迫响应mRNAs，以及异种嫁接对干旱胁迫的及时反应，可以提高南瓜根植物的耐旱性。

原文链接： https://academic.oup.com/hr/article/doi/10.1093/hr/uhab033/6511230?login=false

作者信息：

*南京农业大学园艺学院娄群峰教授和陈劲枫教授为通讯作者，南京农业大学博士研究生Marzieh Davoudi为第一作者。南京农业大学宋蒙飞博士研究生和张孟茹博士研究生共同参与了该研究

  娄群峰个人介绍：

2001.9-2004.7  南京农业大学园艺系 博士研究生

1995.9-1998.7    南京农业大学农学系 硕士研究生

1991.9-1995.7     南京农业大学农学系 本科

2015.1-至今   南京农业大学园艺学院  教授

2008.1-2014.12 南京农业大学园艺学院  副教授

2008.6-2010.1      美国威斯康星大学园艺系  访问学者

2004.9-2007.12 南京农业大学园艺学院    讲师

2001.9-2004.8      江苏农业科学院资源与环境中心  助研

1998.8-2001.8   江苏农业科学院农业现代化研究所 研实

研究方向：长期从事蔬菜遗传育种和细胞分子生物学研究工作

                                                              Journal: Horticulture Research 

Published date: January 19, 2022