Table 1_Transcriptomic and hormonal dynamics in relation to adventitious rooting of two parental Petunia species highlight a coordinated activation of the jasmonate and auxin pathways and an important role of upper-shoot-derived auxin influx.xlsx

IntroductionAdventitious rooting of cuttings is a key developmental process for the vegetative propagation of many crops that involves phytohormone-controlled reprogramming and redifferentiation of specific cells in the stem base. The endogenous control of phytohormone action at the whole-plant level is not completely understood.
MethodsUsing the genome-sequenced Petunia axillaris and Petunia inflata, we monitored the transcriptome of phytohormone-related genes and phytohormone levels in different cutting sections through a phytohormone-targeted microarray, RT-qPCR, and LC-MS/MS, and analyzed the rooting response to manipulations of auxin levels and transport.
ResultsIn the stem base of both species, genes controlling jasmonic acid (JA) biosynthesis, conjugation, and signaling, and encoding transcription factors of the ERF family were already upregulated at 0.5 hours post excision (hpe), followed by increased regulation of auxin-related genes. Accordingly, JA and its physiologically active isoleucine conjugate JA-Ile accumulated transiently at 0.5 hpe, before indole-3-acetic acid (IAA) peaked at 2 hpe. Genes controlling auxin biosynthesis were mostly downregulated, whereas three IAA-leucine-resistant-like genes were strongly upregulated between 0.5 and 2 hpe. P. inflata’s greater rooting capacity compared with P. axillaris was linked to higher stem-base IAA levels (0–72 hpe), resulting in a higher IAA/cytokinin ratio and stronger upregulation of auxin-signaling genes. P. inflata showed a steeper IAA gradient between the leaves and the stem base, which was positively and negatively correlated with leaf salicylic acid and cytokinin isopentenyladenine levels, respectively, and associated with exclusive upregulation of PIN-like genes in the leaves. P. axillaris showed a stronger improvement in rooting with low IAA doses than P. inflata. Blocking polar auxin transport in the upper shoot prevented rooting in both species.
DiscussionThe results reveal excision-triggered coordination of jasmonate and auxin pathways in the stem base, interacting with ERF transcription factors, and indicate an important role for upper shoot-derived auxin influx, potentially regulated by salicylic acid and cytokinins. Higher rooting capacity of P. inflata can be explained by the higher IAA level in the stem base. The results indicate important roles of ERF113/114, ILR-like2 and 6, PIN6, PIN-like 1/3, the PINOID gene A4A49_10797, ARF11, and several LBD genes in adventitious rooting of Petunia.

【引言】插条不定根发生是众多作物无性繁殖的关键发育过程，该过程涉及植物激素（phytohormone）介导的茎基部特定细胞的重编程与再分化。目前学界尚未完全阐明全植株水平上植物激素作用的内源调控机制。
【方法】本研究以基因组已测序的腋蕊矮牵牛（*Petunia axillaris*）和渐叶矮牵牛（*Petunia inflata*）为材料，通过植物激素靶向微阵列、实时定量聚合酶链式反应（RT-qPCR）、液相色谱-串联质谱（LC-MS/MS）技术，监测不同插条区段中植物激素相关基因的转录组水平与植物激素含量，并分析插条生根对生长素（auxin）水平及运输调控的响应。
【结果】在两个矮牵牛物种的茎基部中，控制茉莉酸（jasmonic acid, JA）生物合成、缀合与信号通路，以及编码乙烯响应因子（ERF）家族转录因子的基因均在切除后0.5小时（hours post excision, hpe）即出现上调，随后生长素相关基因的调控水平升高。相应地，茉莉酸及其生理活性缀合物茉莉酸-异亮氨酸（JA-Ile）在0.5 hpe时瞬时积累，而吲哚-3-乙酸（indole-3-acetic acid, IAA）则在2 hpe时达到峰值。控制生长素生物合成的基因大多出现下调，而3个抗IAA-亮氨酸类基因（IAA-leucine-resistant-like genes）在0.5至2 hpe间被显著上调。相较于腋蕊矮牵牛，渐叶矮牵牛具有更强的生根能力，这与其茎基部更高的IAA水平（0~72 hpe）相关，进而形成更高的IAA/细胞分裂素（cytokinin）比值，并使生长素信号通路基因出现更强的上调表达。渐叶矮牵牛的叶片与茎基部之间的IAA梯度更陡，该梯度分别与叶片水杨酸（salicylic acid）含量呈正相关、与叶片细胞分裂素异戊烯基腺嘌呤（isopentenyladenine）含量呈负相关，且与叶片中PIN类基因（PIN-like genes）的特异性上调表达相关。相较于渐叶矮牵牛，低剂量IAA处理可使腋蕊矮牵牛的生根能力得到更显著的提升。阻断地上茎的生长素极性运输（polar auxin transport）后，两个物种的插条均无法生根。
【讨论】本研究结果揭示，插条切除可触发茎基部茉莉酸通路与生长素通路的协同调控，且该过程与ERF转录因子相互作用；同时表明地上茎来源的生长素内流发挥重要作用，该过程可能受水杨酸与细胞分裂素调控。渐叶矮牵牛更强的生根能力可通过其茎基部更高的IAA水平得以解释。本研究结果还明确了ERF113/114、类吲哚乙酸-亮氨酸水解酶（ILR-like）2和6、PIN6、PIN类1/3、PINOID基因A4A49_10797、生长素响应因子（ARF）11以及多个LBD基因（LBD genes）在矮牵牛不定根发生过程中的关键调控作用。