AUTHOR=Lin Yuling , Lin Lixia , Lai Ruilian , Liu Weihua , Chen Yukun , Zhang Zihao , XuHan Xu , Lai Zhongxiong 

TITLE=MicroRNA390-Directed TAS3 Cleavage Leads to the Production of tasiRNA-ARF3/4 During Somatic Embryogenesis in Dimocarpus longan Lour

JOURNAL=Frontiers in Plant Science

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2015.01119

DOI=10.3389/fpls.2015.01119

ISSN=1664-462X

ABSTRACT=<p><italic>Trans</italic>-acting short-interfering RNAs (tasiRNAs) originate from <italic>TAS3</italic> families through microRNA (miRNA) 390-guided cleavage of primary transcripts and target auxin response factors (ARF3/-4), which are involved in the normal development of lateral roots and flowers in plants. However, their roles in embryo development are still unclear. Here, the pathway miR390-<italic>TAS3</italic>-<italic>ARF3</italic>/<italic>-4</italic> was identified systematically for the first time during somatic embryo development in <italic>Dimocarpus longan</italic>. We identified the miR390 primary transcript and promoter. The promoter contained <italic>cis</italic>-acting elements responsive to stimuli such as light, salicylic acid, anaerobic induction, fungal elicitor, circadian control, and heat stress. The longan <italic>TAS3</italic> transcript, containing two miR390-binding sites, was isolated; the miR390- guided cleavage site located near the 3′ end of the <italic>TAS3</italic> transcript was verified. Eight <italic>TAS3</italic>-tasiRNAs with the 21-nucleotides phase were found among longan small RNA data, further confirming that miR390-directed <italic>TAS3</italic> cleavage leads to the production of tasiRNA in longan. Among them, TAS3_5′D5+ and 5′D6+ tasiRNAs were highly abundant, and verified to target <italic>ARF3</italic> and <italic>-4</italic>, implying that miR390-guided <italic>TAS3</italic> cleavage with 21-nucleotides phase leading to the production of tasiRNA-ARF is conserved in plants. Pri-miR390 was highly expressed in friable-embryogenic callus (EC), and less expressed in incomplete compact pro-embryogenic cultures, while miR390 showed its lowest expression in EC and highest expression in torpedo-shaped embryos (TEs). <italic>DlTAS3</italic> and <italic>DlARF4</italic> both exhibited their lowest expressions in EC, and reached their peaks in the globular embryos stage, which were mainly inversely proportional to the expression of miR390, especially at the globular embryos to cotyledonary embryos (CEs) stages. While <italic>DlARF3</italic> showed little variation from the EC to TEs stages, and exhibited its lowest expression in the CEs stage. There was a general lack of correlation between the expressions of <italic>DlARF3</italic> and miR390. In addition, pri-miR390, <italic>DlTAS3</italic>, <italic>DlARF3</italic> and <italic>-4</italic> were up-regulated by 2,4-<sc>D</sc> in a concentration-dependent manner. They were also preferentially expressed in roots, pulp, and seeds of ‘Sijimi’ longan, implying their extended roles in the development of longan roots and fruit. This study provided insights into a possible role of miR390-tasiRNAs-ARF in plant somatic embryo development.</p>