Okazaki Karin, Katano Wataru, Shibata Kyomi, Asahina Masashi, Koshiba-Takeuchi Kazuko, Shimomura Koichiro, Umehara Mikihisa
Graduate School of Life Sciences, Toyo University, Asaka-shi, Saitama, Japan.
Department of Biosciences, Teikyo University, Utsunomiya, Tochigi, Japan.
Physiol Plant. 2025 Jan-Feb;177(1):e70023. doi: 10.1111/ppl.70023.
In many plant species, the application of exogenous phytohormones is crucial for initiating de novo shoot regeneration. However, ipecac [Carapichea ipecacuanha (Brot) L. Andersson] has a unique ability to develop adventitious shoots on the epidermis of internodal segments without phytohormone treatment. This characteristic allows us to evaluate the effects of endogenous phytohormones in this species. Here, we showed that the presence of the pith, including vascular bundles in the internodal segment, is required to activate both endogenous cytokinin (CK) biosynthesis and adventitious shoot formation. Adventitious shoots were mainly formed in the apical region of internodal segments, where the CK biosynthesis genes ISOPENTENYL TRANSFERASE 3 (CiIPT3) and LONELY GUY 7 (CiLOG7) were spontaneously upregulated in the early culture stage on phytohormone-free medium. In addition, CiIPT3 and CiLOG7 were respectively expressed in the pith and the epidermis of the internodal segments. The expression of CiLOG7 was localized as several spots on the epidermis. These findings suggest that CK precursors are generated in the pith, transferred to the epidermis, and then converted into active CKs, facilitating adventitious shoot formation on the epidermis. Conversely, auxin levels rapidly decreased during culture and remained low in the region of shoot formation. Auxin is transferred to the basal region of internodal segments, and strongly suppressed the CiLOG7 expression and decreased the CK levels. Thus, we conclude that the ectopic expression of CiLOG7 in the epidermis of internodal segments contributes to de novo shoot regeneration in ipecac.
在许多植物物种中，外源植物激素的应用对于从头开始的芽再生至关重要。然而，吐根（Carapichea ipecacuanha (Brot) L. Andersson）具有独特的能力，即在不进行植物激素处理的情况下，能在节间段的表皮上发育不定芽。这一特性使我们能够评估该物种中内源植物激素的作用。在此，我们表明，髓的存在，包括节间段中的维管束，对于激活内源细胞分裂素（CK）生物合成和不定芽形成都是必需的。不定芽主要在节间段的顶端区域形成，在无植物激素培养基上的早期培养阶段，CK生物合成基因异戊烯基转移酶3（CiIPT3）和孤独家伙7（CiLOG7）在该区域自发上调。此外，CiIPT3和CiLOG7分别在节间段的髓和表皮中表达。CiLOG7的表达定位在表皮上的几个斑点处。这些发现表明，CK前体在髓中产生，转移到表皮，然后转化为活性CK，促进表皮上不定芽的形成。相反，在培养过程中生长素水平迅速下降，并且在芽形成区域保持较低水平。生长素转移到节间段的基部区域，并强烈抑制CiLOG7的表达并降低CK水平。因此，我们得出结论，CiLOG7在节间段表皮中的异位表达有助于吐根的从头芽再生。
