Gender-specific expression of GIBBERELLIC ACID INSENSITIVE is critical for unisexual organ initiation in dioecious Spinacia oleracea

• While unisexual flowers (单性花) have evolved repeatedly throughout angiosperm families, the actual identification of sex-determining genes has been elusive, and their regulation within populations remains largely undefined. Here, we tested the mechanism of the feminization (雌性化) pathway in cultivated spinach (Spinacia oleracea; 菠菜), and investigated how this pathway may regulate alternative sexual development.

• We tested the effect of gibberellic acid (GA) on sex determination through exogenous (外源的) applications of GA and inhibitors of GA synthesis and proteasome activity. GA concentrations in multiple tissues were estimated by enzyme-linked immunosorbent assay (酶联免疫吸附试验) analysis. Gene function was investigated and pathway analysis was performed through virus-induced gene silencing. Relative gene expression levels were estimated by quantitative reverse transcription−polymerase chain reaction (QRT-PCR).

• Inhibition of GA production and proteasome activity feminized male flowers. However, there was no difference in GA content in tissues between males and females. We characterized a single DELLA family transcription factor gene (GIBBERELLIC ACID INSENSITIVE (SpGAI)) and observed inflorescence expression in females two-fold higher than in males. Reduction of SpGAI expression in females to male levels phenocopied exogenous GA application with respect to flower development.

• These results implicate SpGAI as the feminizing factor in spinach, and suggest that the feminizing pathway is epistatic (上位性) to the masculinizing (雄性化) pathway. We present a unified model (统一模型) for alternative sexual development and discuss the implications for established theory.

单性花在被子植物中独立多次发生，然而对于性别决定基因仍然难以鉴定，同时对于这些基因群体内如何起调控作用还不清楚。本文对栽培中菠菜雌性化通路可能的机制进行了检测，并研究了这个通路是如何调控性发育的选择的。

作者通过施加外源性的GA和抑制GA的生物合成和蛋白酶体活性来研究GA对于性别决定的影响。GA在不同组织中的浓度通过酶联免疫吸附试验进行测定和分析。作者还通过病毒诱导的基因沉默来研究参与该通路相关基因的功能。基因的相对表达水平通过QRT-PCR进行测定。

抑制GA的产量和蛋白酶体活性会雌性化雄花。然而，雄性和雌性不同组织中的GA含量却没有差别。作者坚定了一个DELLA家族的转录因子SpGAI基因，并观察到在雌花中该基因的表达是胸花中的两倍。降低雌花中SpGAI基因的表达到雄花中的水平会在花发育方面再现外源GA处理时的表型。

这些结果说明SpGAI可能作为菠菜中雌性化的因子，并且雌性化通路对于雄性化通路表现上位作用。本文给出了性发育选择的统一模型，并讨论了对于现有理论的启示。

通讯：Edward M. Golenberg (http://bio.wayne.edu/profhtml/golen/golenberg.html)

研究方向：栽培菠菜性二形性的发育及雌雄异株的遗传学基础。

doi: 10.1111/nph.14919