The Flavoproteins CryD and VvdA Cooperate with the White Collar Protein WcoA in the Control of Photocarotenogenesis in Fusarium fujikuroi

Light stimulates carotenoid biosynthesis in the ascomycete fungus Fusarium fujikuroi through transcriptional activation of the structural genes of the pathway carRA, carB, and cart, but the molecular basis of this photoresponse is unknown. The F. fujikuroi genome contains genes for different predicted photoreceptors, including the WC protein WcoA, the DASH cryptochrome CryD and the Vivid-like flavoprotein VvdA. We formerly found that null mutants of wcoA, cryD or vvdA exhibit carotenoid photoinduction under continuous illumination. Here we show that the wild type exhibits a biphasic response in light induction kinetics experiments, with a rapid increase in carotenoid content in the first hours, a transient arrest and a subsequent slower increase. The mutants of the three photoreceptors show different kinetic responses: the wcoA mutants are defective in the rapid response, the cryD mutants are affected in the slower response, while the fast and slow responses were respectively enhanced and attenuated in the vvdA mutants. Transcriptional analyses of the car genes revealed a strong reduction of dark and light-induced transcript levels in the wcoA mutants, while minor or no reductions were found in the cryD mutants. Formerly, we found no change on carRA and carB photoinduction in vvdA mutants. Taken together, our data suggest a cooperative participation of WcoA and CryD in early and late stages of photoinduction of carotenoid biosynthesis in F. fujikuroi, and a possible modulation of WcoA activity by VvdA. An unexpected transcriptional induction by red light of vvdA, cryD and carRA genes suggest the participation of an additional red light-absorbing photoreceptor.

光可通过激活类胡萝卜素生物合成通路的结构基因carRA、carB及cart的转录，促进子囊菌门真菌藤仓镰孢霉(Fusarium fujikuroi)的类胡萝卜素生物合成，但该光响应的分子基础尚未阐明。藤仓镰孢霉的基因组编码多种预测的光受体，包括WC蛋白(WcoA)、DASH隐花色素(CryD)以及Vivid类黄素蛋白(VvdA)。我们此前发现，wcoA、cryD或vvdA的缺失突变体在持续光照下仍可发生类胡萝卜素的光诱导。本研究显示，野生型菌株在光诱导动力学实验中呈现双相响应：最初数小时内类胡萝卜素含量快速升高，随后出现短暂停滞，继而又呈现较为缓慢的含量升高。三种光受体的缺失突变体展现出不同的动力学响应特征：wcoA突变体的快速响应存在缺陷，cryD突变体的缓慢响应受到影响，而vvdA突变体的快速响应与缓慢响应则分别被增强与减弱。对car类基因的转录分析结果显示，wcoA突变体中黑暗及光诱导的转录本水平均显著降低，而cryD突变体中仅出现轻微降低或无明显变化。我们此前曾发现，vvdA突变体中carRA与carB的光诱导水平无明显变化。综上，我们的研究数据表明，WcoA与CryD在藤仓镰孢霉类胡萝卜素生物合成光响应的早期与晚期阶段发挥协同作用，且VvdA可能对WcoA的活性具有调控功能。红光对vvdA、cryD及carRA基因的意外转录诱导提示，该真菌中还存在另一种可吸收红光的光受体。