DH2-dependent trans-acting siRNAs regulate leaf and lemma development in rice

In most crops, the development of lateral organs such as leaves and floral organs plays important roles in the architecture of plants and grains and then determines the yield. Establishment of polarity in these lateral organs is one of the most critical events for their morphogenesis. However, the molecular mechanisms regarding this in rice remain unclear. Here, we isolated two allelic mutants named <i>degenerated hull 2-1</i> and <i>degenerated hull 2-2</i> (<i>dh2-1</i> and <i>dh2-2</i>) in rice, exhibiting abaxially rolled leaves and rod-shaped lemmas. <i>DH2</i> encoded the relatively conservative ARGONAUT 7 (AGO7) protein in plants and expressed in the lateral organs including leaf and floral organs. In addition, the overexpression lines of <i>DH2</i> showed adaxially rolled leaves. Next, it was proved that <i>DH2</i> was involved in the synthesis of <i>tasiR-ARFs</i>, the expression level of which was decreased sharply in lateral organs of <i>dh2</i> mutants. Then, it was found that the expression of <i>OsARF2, OsARF3, OsARF14</i>, and <i>OsARF15</i>, the potential targets of <i>tasiR-ARFs</i>, was increased in lateral organs of <i>dh2</i> mutants. However, it was not expected that the results of <i>in situ</i> hybridization showed that the four <i>ARF</i> genes were not expressed in WT lemma, whereas they were all ectopically expressed in rod-shaped lemma in <i>dh2</i> mutants. Meanwhile, <i>tasiR-ARFs</i> were expressed in the whole lemma but not in the abaxial side. This means that there was no opposite expression of <i>tasiR-ARFs</i> and <i>ARFs</i> in the adaxial-abaxial of lemma. Therefore, according to our data, we believe that the pathway of OsAGO7-tasiR-ARFs in rice was more likely involved in the development of the whole lemma, not only the abaxial side, by restricting the ectopic expression of <i>OsARFs</i> in the whole lemma, which was different from that in the lateral organs of Arabidopsis.