**4.4. RNA-dependent DNA methylation**

The modification of chromatin is facilitated by recruitment of chromatin modifiers through lncRNA and small RNA (sRNA) into the specific locations in DNA. This RNA-dependent DNA methylation (RdDM) is a conserved process that recruits DNA methyltransferase and histone modifiers for DNA methylation and suppressive histone modification, respectively [59].

## **4.5. Chromosome looping**

This mechanism is different from RdDM and histone modification, as it only involves the structural changes of chromatin. Thereby, it affects the binding potential of RNA polymerase and other transcription factors [60]. A persuasive example of chromosome looping mechanism in plants by *APOLO* lncRNA has been described in auxin transport by regulating the PID expression, an auxin transporter. When locus of *APOLO* lncRNA is transcribed by RNA Pol V and modified by RdDM, the expression of the locus is suppressed and loops to PID. This causes the inhibition of PID transcription. In contrast, when RNA Pol II carry out the transcription of APOLO lncRNA the looping of PID is restrained resulting in the expression of PID [60].
