Transcriptional changes in Aspergillus flavus-infected maize kernels

Maize kernels are susceptible to infection by the opportunistic pathogen Aspergillus flavus. Infection results in reduction of grain quality and contamination of kernels with the highly carcinogenic mycotoxin, aflatoxin. To understand host response to infection by the fungus, transcription of approximately 9,000 maize genes were monitored during the host-pathogen interaction with a custom-designed Affymetrix GeneChip® DNA array. More than 1,000 maize genes were found differentially expressed at a fold change of 2 or greater. This included the up regulation of defense-related genes and signaling pathways. Transcriptional changes also were observed in primary metabolism genes. Starch biosynthetic genes were down regulated during infection, while genes encoding maize hydrolytic enzymes, presumably involved in the degradation of host reserves, were up regulated. These data indicate that infection of the maize kernel A. flavus induced metabolic changes in the kernel, including the production of a defense response, as well as a disruption in kernel development. Maize kernels were mock inoculated at the blister (R2) or dough (R4) stage or inoculated with A. flavus at the blister (R2), milk (R3), dough (R4), or dent (R5) stage, and harvested 4 days later. Each treatment consisted of three biological replications. For each biological replication, 8 kernels were ground and RNA was isolated and further processed.

玉米籽粒易被机会性致病菌黄曲霉（Aspergillus flavus）侵染。该侵染会导致籽粒品质下降，并会被强致癌性真菌毒素黄曲霉毒素（aflatoxin）污染。为解析宿主对该真菌侵染的应答反应，本研究通过定制化Affymetrix GeneChip® DNA芯片，在宿主-病原菌互作过程中对约9000个玉米基因的转录水平进行了监测。最终发现超过1000个玉米基因的表达差异倍数达到2倍及以上，其中包含防御相关基因与信号通路的上调表达。初级代谢相关基因同样出现了转录水平的变化：淀粉生物合成基因在侵染过程中被下调，而编码玉米水解酶（推测参与宿主储备物质降解）的基因则被上调。上述数据表明，黄曲霉侵染玉米籽粒会诱导籽粒发生代谢变化，包括激活防御应答反应，同时也会干扰籽粒发育进程。
本研究分别在疱粒期（R2）、蜡熟期（R4）对玉米籽粒进行空白接种处理，同时在疱粒期（R2）、乳熟期（R3）、蜡熟期（R4）及硬熟期（R5）用黄曲霉进行接种处理，并于接种4天后收获样本。每组处理设置3次生物学重复；每次生物学重复选取8粒籽粒进行研磨，随后提取RNA并完成后续实验处理。