SPL7 and SPL8 represent a novel flowering regulation mechanism in switchgrass

First author: Jiqing Gou; Affiliations: Noble Research Institute (诺布尔研究所): Ardmore, USA

Corresponding author: Zeng‐Yu Wang

The aging pathway in flowering regulation is controlled mainly by microRNA156 (miR156). Studies in Arabidopsis thaliana reveal that nine miR156‐ argeted SQUAMOSA PROMOTER BINDING‐LIKE (SPL) genes are involved in the control of flowering. However, the roles of SPLs in flowering remain elusive in grasses. Inflorescence development in switchgrass was characterized using scanning electron microscopy (SEM). Microarray, quantitative reverse transcription polymerase chain reaction (qRT‐PCR), chromatin immunoprecipitation (ChIP)‐PCR and EMSA were used to identify regulators of phase transition and flowering. Gene function was characterized by downregulation and overexpression of the target genes. Overexpression of SPL7 and SPL8 promotes flowering, whereas downregulation of individual genes moderately delays flowering. Simultaneous downregulation of SPL7/SPL8 results in extremely delayed or nonflowering plants. Furthermore, downregulation of both genes leads to a vegetative‐ o‐ eproductive reversion in the inflorescence, a phenomenon that has not been reported in any other grasses. Detailed analyses demonstrate that SPL7 and SPL8 induce phase transition and flowering in grasses by directly upregulating SEPALLATA3 (SEP3) and MADS32. Thus, the SPL7/8 pathway represents a novel regulatory mechanism in grasses that is largely different from that in Arabidopsis. Additionally, genetic modification of SPL7 and SPL8 results in much taller plants with significantly increased biomass yield and sugar release.

开花调控的年龄途径主要由miR156所控制。拟南芥中的研究显示9个miR156靶向的SPL基因参与了开花调控。然而，草类植物SPL基因在开花过程中的作用还不清楚。作者通过扫描电子显微镜观察了柳枝稷的花序发育特征。作者通过芯片、qRT‐PCR、ChIP‐PCR和EMSA试验鉴定了柳枝稷中与开花相关的调控因子。作者进一步通过对靶基因的上、下调来验证了基因的功能。SPL7和SPL8的过表达能够促进开花，而单独下调SPL7或SPL8基因的表达能够在一定程度上延迟开花。同时下调SPL7/SPL8的表达会导致植株晚花，甚至不开花。此外，同时下调这两个基因会导致花序组织营养生长向生殖生长的逆转，这一现象在其它的草类植物中还未曾见报道。进一步的分析揭示了SPL7和SPL8通过直接上调SEP3和MADS32基因的表达来诱导植株开花。因此，本文鉴定了草类植物中一个新的调控开花途径的通路SPL7/8，这与拟南芥中的完全不一样。另外，SPL7和SPL8的遗传修饰能够导致植株长得更高，且生物量和产糖量显著增加。

doi: https://doi.org/10.1111/nph.15712

Journal: New Phytologist

FIRST Published: January 28, 2019