Department of Fruit Science, College of Horticulture, China Agricultural University, Beijing, 100193, China.
Department of Agricultural Sciences, Viikki Plant Science Centre, University of Helsinki, Latokartanonkaari 7, 00790, Helsinki, Finland.
Plant J. 2022 Jun;110(5):1237-1254. doi: 10.1111/tpj.15759. Epub 2022 Apr 25.
A runner, as an elongated branch, develops from the axillary bud (AXB) in the leaf axil and is crucial for the clonal propagation of cultivated strawberry (Fragaria × ananassa Duch.). Runner formation occurs in at least two steps: AXB initiation and AXB outgrowth. HANABA TARANU (HAN ) encodes a GATA transcription factor that affects AXB initiation in Arabidopsis and promotes branching in grass species, but the underlying mechanism is largely unknown. Here, the function of a strawberry HAN homolog FaHAN in runner formation was characterized. FaHAN transcripts can be detected in the leaf axils. Overexpression (OE) of FaHAN increased the number of runners, mainly by enhancing AXB outgrowth, in strawberry. The expression of the strawberry homolog of BRANCHED1 , a key inhibitor of AXB outgrowth in many plant species, was significantly downregulated in the AXBs of FaHAN -OE lines, whereas the expression of the strawberry homolog of SHOOT MERISTEMLESS, a marker gene for AXB initiation in Arabidopsis, was upregulated. Moreover, several genes of gibberellin biosynthesis and cytokinin signaling pathways were activated, whereas the auxin response pathway genes were repressed. Further assays indicated that FaHAN could be directly activated by FaNAC2, the overexpression of which in strawberry also increased the number of runners. The silencing of FaNAC2 or FaHAN inhibited AXB initiation and led to a higher proportion of dormant AXBs, confirming their roles in the control of runner formation. Taken together, our results revealed a FaNAC2-FaHAN pathway in the control of runner formation and have provided a means to enhance the vegetative propagation of cultivated strawberry.
匍匐茎作为一个细长的分支，从叶腋的腋芽（AXB）发育而来，对栽培草莓（Fragaria ×ananassa Duch.）的克隆繁殖至关重要。匍匐茎的形成至少需要两个步骤：AXB 的起始和 AXB 的延伸。HANABA TARANU（HAN）编码一个 GATA 转录因子，它影响拟南芥 AXB 的起始并促进禾本科植物的分枝，但基本机制尚不清楚。在这里，我们研究了草莓 HAN 同源物 FaHAN 在匍匐茎形成中的功能。FaHAN 转录本可以在叶腋中检测到。草莓 FaHAN 的过表达（OE）增加了匍匐茎的数量，主要是通过增强 AXB 的延伸。在 FaHAN-OE 系中，草莓 BRANCHED1 同源物的表达，该基因是许多植物物种 AXB 延伸的关键抑制剂，显著下调，而草莓 SHOOT MERISTEMLESS 同源物的表达，拟南芥 AXB 起始的标记基因，上调。此外，几种赤霉素生物合成和细胞分裂素信号通路的基因被激活，而生长素响应途径的基因被抑制。进一步的实验表明，FaHAN 可以被 FaNAC2 直接激活，草莓中 FaNAC2 的过表达也增加了匍匐茎的数量。FaNAC2 或 FaHAN 的沉默抑制了 AXB 的起始，并导致休眠 AXB 的比例更高，这证实了它们在控制匍匐茎形成中的作用。总之，我们的研究结果揭示了一个 FaNAC2-FaHAN 途径在控制匍匐茎形成中的作用，并提供了一种增强栽培草莓营养繁殖的方法。
