Question

the fungus *fusarium fujikuroi* (*f. fujikuroi*) is a plant pathogen that can infect and destroy corn crops. some corn varieties are less susceptible to *f. fujikuroi* than others. a recent study showed that less-susceptible varieties produced and exported an mirna that targets the fungal gene *root*. thee mirna produced and exported from the corn and then taken up by *f. fujikuroi*. this mirna is completely complementary to a highly conserved region of the *root* coding sequence. in fungi such as *f. fujikuroi* the *rrot* gene codes for transcriptional co-activator. like many co-activators, *rrot* is a protein that assists transcription factors in binding to dna. even though the mirna is highly specific to the mrna of the *rrot* gene, researchers found that when *f. fujikuroi* was exposed to this mirna expression of a number of other genes in the fungus were down-regulated. explain how expression of genes other than *rrot* could be down-regulated.

Answer 1

The down-regulation of genes beyond the specific target, the rrot gene in Fusarium fujikuroi, is likely due to the ripple effect that inhibiting a transcriptional co-activator has on the transcriptional network. Interference by the corn miRNA can broadly affect the fungal genes that rely on the regulatory functions of rrot, leading to a suppression cascade affecting multiple genes.

Step-by-step explanation:

The down-regulation of genes other than rrot in Fusarium fujikuroi when exposed to corn miRNA can be attributed to a complex network of gene regulation. The targeted suppression of the rrot gene, which codes for a transcriptional co-activator, can lead to a cascade of transcriptional changes affecting other genes. The co-activator protein assists in transcription factor binding to DNA; thus, inhibiting its function can disrupt the transcription of multiple genes that rely on this regulatory pathway.

This can indirectly cause down-regulation of various other genes involved in fungal growth and virulence, which rely on the proper functioning of rrot. Additionally, plants utilize complex defense strategies, including the production of small RNAs like miRNAs, which are involved in gene silencing mechanisms that can target multiple aspects of pathogen infection, spreading the effect beyond a single gene target. This miRNA interference illustrates the intricate ways in which plants can defend themselves against pathogens, such as F. fujikuroi.