**3.2 Phosphate**

Phosphate-responsive sRNA involved in Pi-uptake, transport, assimilation and homeostasis through targeting mRNA transcripts are extensively studied and identified in plant including rice, maize, tomato, soybean and Arabidopsis [29–33]. Among these plant species, common set of plant miRNA families are characterized modulating signaling networks, including miRNA156, miRNA159, miRNA166, miRNA319, miRNA395, miRNA398, miRNA399, miRNA447, and miRNA827 are demonstrated in response to Pi-limiting environment [34, 35]. An elevated level of miRNA156, miRNA399, miRNA778, miRNA827, miRNA2111 and suppressed miRNA169, miRNA395 and miRNA398 levels are observed under Pi stress [28]. Role of miRNA2111 has been illustrated under N and Pi limiting conditions [36]. The expression of phosphate-responsive PHO2 transporter was altered by miRNA827 and miRNA399 [37]. Moreover, miRNA827 targets the Major Facility Superfamily (MFS)- XPS proteins which are involved in Pi sensing and transport [38]. Common response against nutrient starvation includes anthocyanin accumulation in plants. MYB TF regulated anthocyanin biosynthesis pathway genes are targeted by siRNAs produced by ta-siRNA4 under the regulation of Pi-responsive miRNA828, post-transcriptionally [39]. The major regulatory role in maintenance of mineral homeostasis in host plant under N, Pi and C limiting environments is performed by miRNA398a [40]. Among all the characterized Pi-responsive miRNAs, altered levels of different alleles of miRNA399 were found conserved and pre-dominant under Pi-limiting conditions [41]. miRNAs and siRNAs induction was reported upon *Candidatus liberibacter* infection in citrus plants and interestingly, miRNA399 level was found elevated in infected plants than healthy host under Pi-limiting conditions [33]. These facts demonstrate the critical role of sRNAs in post-transcription regulation of Pi-responsive transcripts enabling host adaption under nutrition stress.

#### **3.3 Sulfate**

Sulfate transporters located on root epidermal and cortical cell membrane are the key components in sulfur uptake and transport to the plants in SO42− form. Based on their substrate affinity, sequence similarity and their location of expression, they

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

are categorized into five major groups. Group 1, group 2 and group 3 are characterized as high affinity, low affinity, and moderate affinity transporters for sulfur substrate, respectively [42–44]. Group 4 and 5 transporters are characterized as efflux transporter on tonoplast and molybdenum transporters (for being actively involved in molybdenum transport across the plant) respectively [45, 46]. S uptake from soil to the root is carried out by group1 and 2 transporters, while root to shoot transport of S is done by group 4 transporters. Under S-limiting conditions plethora of miRNAs induced including miRNA66, miRNA67 and miRNA395 while suppression of miRNA14, miRNA20 and miRNA43 is associated with regulation of posttranscription modification of S signaling. miRNA395 is a S-specific ncRNA signal and has been characterized to function as a key regulator of the sulfate depletion pathway. Under S-deprivation, miRNA395 positively regulates the expression of the low-affinity transporter AtSul2;1 [47], supporting sulfate uptake and transport of cells to shoots and leaves in *Arabidopsis thaliana*. The initial step of S assimilation into cysteine is catalyzed by ATP dependent sulphurylases (APSs), which are the target for miRNA395 in plastids [35].
