Expression Analysis Of MiRNAs And Highly-expressed Small RNAs In Two Rice Subspecies And Their Reciprocal Hybrids

Heterosis, or hybrid vigor, is the phenomenon whereby progeny of two inbred lines exhibit superior agronomic performance compared to either parent. We analyzed the expression of miRNAs and highly expressed small RNAs (defined according to Solexa sequencing results) in two rice (Oryza sativa) subspecies (Nipponbare and 93-11) and their reciprocal hybrids using microarrays. We found that of all the 1141 small RNAs tested,140 (12%,140 out of 1142) and 157 (13%,157 out of 1142) were identified being significantly differentially expressed in two reciprocal hybrids, respectively. All possible modes of action, including additive, high-and low-parent, above high-and below low-parent modes were exhibited. Both F1 hybrids showed non-additive expression patterns, with down-regulation predominating. Interestingly,15 miRNAs displayed stark opposite expression trends relative to mid-parent in reciprocal hybrids. Computational prediction of differentially expressed miRNAs targets showed that they participated in multifaceted developmental pathways and were not distinguishable from non-differentially expressed miRNAs targets. Together, our findings reveal that small RNAs play roles in heterosis and add a new layer in the understanding and exploitation of molecular mechanisms of heterosis.