Genome-wide profiling of populus small RNAs

Area of Science:

• Plant molecular biology
• Transcriptomics
• Epigenetics

Background:

• Short RNAs (sRNAs), including microRNAs (miRNAs), are key regulators of gene expression.
• Investigating the sRNA population in Populus trichocarpa (black cottonwood) is crucial for understanding its gene regulation.
• The sequenced genome of P. trichocarpa provides a basis for genome-wide sRNA analysis.

Purpose of the Study:

• To characterize the short RNA (sRNA) population (18-24 nt) in green leaves of Populus trichocarpa.
• To identify novel microRNAs (miRNAs) and small interfering RNAs (siRNAs) in this species.
• To provide a genome-wide perspective on sRNA production in P. trichocarpa.

Main Methods:

• Utilized a concatenation strategy combined with 454 sequencing to analyze the sRNA transcriptome.
• Focused on the 18-24 nucleotide size range of sRNAs.
• Bioinformatic analysis to identify sRNA loci, miRNA precursors, and potential targets.

Main Results:

• The most abundant sRNA size class observed was 24 nucleotides.
• Long Terminal Repeats (LTRs) were significantly associated with 24 nt sRNAs, and other repetitive elements with 22 nt sRNAs.
• Identified 15 novel predicted miRNAs, including miRNA* sequences, and a unique locus potentially encoding dual miRNAs or miRNA/siRNAs. An sRNA hotspot on chromosome 19 was noted, overlapping with the sex-determining locus and NBS-LRR genes.
• Discovered phased siRNA loci targeting disease resistance genes (PPR and NBS-LRR), which are expanded in Populus.

Conclusions:

• The short RNA population of Populus trichocarpa is highly complex, comparable to Arabidopsis thaliana.
• This study presents the first genome-wide landscape of short RNA production in P. trichocarpa.
• New, non-conserved microRNAs were identified, expanding the known repertoire of regulatory RNAs in this species.