背景回顾：Under field conditions, plants are often simultaneously exposed to several abiotic and biotic stresses resulting in significant reductions in growth and yield; thus, developing a multi-stress tolerant variety is imperative. Previously, we reported the neofunctionalization of a novel PNP family protein, Putranjiva roxburghii purine nucleoside phosphorylase (PRpnp) to trypsin inhibitor to cater to the needs of plant defense. 

提出问题：However, to date, no study has revealed the potential role and mechanism of either member of this protein group in plant defense. 

主要发现：Here, we overexpressed PRpnp in Citrus aurantifolia which showed nuclear-cytoplasmic localization, where it functions in maintaining the intracellular purine reservoir. 

结果1-抗性增强：Overexpression of PRpnp significantly enhanced tolerance to salt, oxidative stress, alkaline pH, drought, and two pests, Papilio demoleus and Scirtothrips citri in transgenic plants. 

结果2-基因表达谱：Global gene expressionstudies revealed that PRpnp overexpression up-regulated differentially expressed genes (DEGs) related to ABA- and JA- biosynthesis and signaling, plant defense, growth, and development. 

结果3-代谢图谱：LC-MS/MS analysis validated higher endogenous ABA and JA accumulation in transgenic plants.

结论：Taken together, our results suggest that PRpnp functions by enhancing the endogenous ABA and JA, which interact synergistically and it also inhibits trypsin proteases in the insect gut. Also, like other purine salvage genes, PRpnp also regulates CK metabolism and increases the levels of CK-free bases in transgenic Mexican lime. We also suggest that PRpnp can be used as a potential candidate to develop new varieties with improved plant vigor and enhanced multiple stress resistance.

Leaf disc senescence assays showed enhanced multiple stress tolerance in PRpnp transgenic C. aurantifolia.

在大田条件下，植物通常会同时遭受多种生物和非生物胁迫，从而导致生长和产量的巨大损失；因此，开发具有多种胁迫抗性品种的需求十分迫切。作者在先前的研究中报道了一个新的PNP家族蛋白的新功能化，即印度假黄杨嘌呤核苷磷酸化酶PRpnp作为胰蛋白酶抑制剂满足植物防御的需求。但是，目前为止还没有研究报道该蛋白成员在植物防御中的潜在作用及机理。本文中，作者在来檬中过表达了PRpnp基因，表现出核质定位，作用于胞内嘌呤库的维持。PRpnp过表达能够显著增强转化植株对盐、氧化胁迫、碱性pH、干旱以及非洲达摩凤蝶和柑橘蓟马两种害虫的抗性。基因表达谱显示PRpnp过表达引起的差异表达基因主要与ABA和JA生物合成及信号转导、植物防御、生长和发育有关。液相色谱-串联质谱联用（LC-MS/MS）分析显示转化植株中含有更高含量的ABA和JA。综上，本文的研究结果揭示了PRpnp通过增强内源性的ABA和JA发挥作用，同时还能够抑制害虫肠道中的胰蛋白酶。另外，与其他嘌呤基因一样，PRpnp能够调控细胞分裂素（CK）代谢，增加转基因墨西哥酸橙中的游离CK水平。因此，PRpnp可以作为潜在候选基因，用于开发生长活力强和高抗的植物新品种。

** Harsh Chauhan **