**5. Plant's ncRNAs modulating interconnection networks with fungi**

#### **5.1 miRNA**

In recent past decades, the focus has pushed beyond the traditional defense pathway's transcriptional control in establishing pathogenic or beneficial plant-microbe interactions to attempts to understand novel transcriptional regulators. In particular, many groups have started investigating the function of microRNAs (miRNAs) in regulating signaling processes accompanying the symbiotic interactions. Many plant miRNAs have been reported to be involved in modulating the plant-pathogenic microbe interactions. The majority of miRNAs investigated and characterized to date complements the alterations described well in the transcriptome. For example, one of the defenses against necrotrophic pathogens involves improving the physical tolerance of plant cells. *Arabidopsis* miRNA408 and miRNA160a induce physical cell reinforcement by positive regulation of lignification and callose deposition [74, 75]. In *Medicago* and *Oriza*, various miRNA targets the ET (Ethylene), JA (Jasmonic Acid), and SA (Salicylic Acid) biogenesis during pathogenesis at very early stages [76, 77]. During attack by biotrophic pathogens, many miRNAs also suppress routine cellular detoxification. One example is miRNA398, which enhances ROS generation in *Magnaporthe oryzae*-infected tissues [78]. On the other hand, in case of tomato, the necrotrophic association between plant and *Alternaria solani*, miRNAs target gene transcripts are reported to be actively involved in toxin detoxification [79]. This suggests that miR-NAs have potential to modify plant cells into the toxic ecosystems, poisoning invading microbes before they spread further to strengthen host immunity.

In mutual bio-trophic interactions, a few recent investigations have shown that the a major proportion of miRNAs synthesized all through interaction establishment

#### *Role of Non-Coding RNAs in Plant Nutrition through Mycorrhizal Interactions DOI: http://dx.doi.org/10.5772/intechopen.108517*

modulate hormone response pathways, protein methylation, and functions of innate immunity components [78, 80]. A well-studied example includes the miRNA (annotated as E4D3Z3Y01BW0TQ ) which is reported to be induced during AM symbiosis progression and interferes with GA signaling. GA signaling pathway is known to inhibit symbiotic-association [81–83]. On the other hand, miRNA172c promotes nodule formation in many plants by repressing the translation of APETALA2 TF [84, 85]. In AM-colonized roots, miRNA171b hampers with GRAS TF-responsive transcripts targeting through miRNA171, which are necessary for both nodulation and symbiosis.

#### **5.2 siRNA**

Microorganisms can have a significant impact on how plants react to colonization; they are not just background actors in the process. Since past few decades, effector proteins and siRNAs have been the two main areas of research. A variety of plant signaling pathways are altered by microbial effector proteins, which are generally tiny secreted proteins that are substantially stimulated during the colonization process. Similar to effector proteins, siRNAs target essential plant transcripts, disrupt transcripts via the ARGONAUTE (AGO) pathway, or act in a manner resembling that of miRNAs by inhibiting tRNA binding and localization. The microorganism-secreted siRNAs are taken up by the host plant, and disrupt the key transcripts of host.

*Botrytis cinerea*, a fungal pathogen, has been demonstrated to alter plant physiology during colonization by secreting siRNAs [86]. *B. cinerea* siRNAs initially penetrate host plant cells during the pathogenesis of tomato and *Arabidopsis*, where they diminish the host's RNAi apparatus. These relatively tiny molecules can therefore be thought of as variants of conventional effector proteins. In case of *A. thaliana*, *Bc*-siRNA3.1, *Bc*-siRNA3.2, and *Bc*-siRNA5 collectively silenced the stress-related genes, such as PRXIIF, WAK, MPK1 and MPK2 to eliminate the plant defense [87]. However, *Bc*-siRNA37 AtPMR6, AtFEI2 and AtWRKY7 are selectively silenced by *Bc*-siRNA37 [88]. While this is the only example so far in which siRNAs have been formed and released by microbes and reached to the host plant cells, there can be another common means based on genomic analysis by which microbes can modulate host responses during colonization.
