SPL7 and SPL8 represent a novel flowering regulation mechanism in switchgrass

First author: Jiqing Gou; Affiliations: Noble Research Institute (牧草改良中心): Ardmore, USA

Corresponding author: Zeng‐Yu Wang

The aging pathway in flowering regulation is mainly controlled 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 microscope (SEM). Microarray, reverse transcription quantitative (RT‐q)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 while downregulation of individual genes moderately delays flowering. Simultaneous downregulation of SPL7/SPL8 results in extremely delayed or non‐flowering 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 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 8 results in much taller plants with significantly increased biomass yield and sugar release.

开花调控的年龄通路主要受到miR156的调控。拟南芥中的研究显示9个由miR156靶向的SPL基因参与开花调控。然而，SPL基因在草本中调控开花的分子机制还不是很清楚。作者利用电子显微镜研究了柳枝稷中的花絮发育特征。微阵列、反向qRT-PCR、染色质免疫沉淀PCR和EMSA试验经常被用于鉴定植物生长状态转变和开花的调控因子。作者通过下调表达和过表达基因来研究目的基因的功能。过表达SPL7和SPL8能够促进开花，同时下调某些延迟开花基因的表达。同时下调SPL7/SPL8基因的表达量能够延迟植物的开花，或者直接导致植物不开花。此外，同时下调这两个基因的表达量会导致花絮从营养生长向生殖生长的逆转，这种情况在其它植物中还未曾见报道。进一步的研究显示SPL7和SPL8通过直接上调SEP3和MADS32诱导了植物生长状态转变和开花。因此，SPL7/8通路代表了草本植物的一个不同于拟南芥的新的调控植物开花的分子调控机制。另外，SPL7和SPL8的遗传修饰会导致植物增高，同时增加植物生物量和糖产量。

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

Journal: New Phytologist

First Published: January 28, 2019