Abstract
BackgroundPlants have evolved excellent ability of flexibly regulating the growth of organs to adapt to changing environment, for example, the modulation of lateral root development in response to environmental stresses. Despite of fundamental discovery that some microRNAs are involved in this process, the molecular mechanisms of how these microRNAs work together are still largely unknown.ResultsHere we show that miR390 induced by auxin promotes lateral root growth in rice. However, this promotion can be suppressed by miR393, which is induced by various stresses and ABA (Abscisic Acid). Results that miR393 responded to ABA stronger and earlier than other stresses implied that ABA likely is authentic factor for inducing miR393. The transgenic lines respectively over-expressing miR393 and OsTAS3a (Oryza sativa Trans-Acting Short RNA precursor 3a) displayed opposite phenotypes in lateral root growth. MiR390 was found to be dominantly expressed at lateral root primordia and roots tips while miR393 mainly expressed in the base part of roots at very low level. When miR393 was up-regulated by various stresses, miR390 expression level fell down. However, the risen expression level of miR390 induced by auxin didn’t affect the expression of miR393 and its target OsTIR1 (Transport Inhibitor Response 1). Together with analysis of the two transgenic lines, we provide a model of how the growth of lateral roots in rice is regulated distinctively by the 2 microRNAs.ConclusionWe propose that miR390 induced by auxin triggers the lateral root growth under normal growth conditions, meanwhile miR393 just lurks as a potentially regulative role; Once plants suffer from stresses, miR393 will be induced to negatively regulate miR390-mediated growth of lateral roots in rice.
Highlights
Plants have evolved excellent ability of flexibly regulating the growth of organs to adapt to changing environment, for example, the modulation of lateral root development in response to environmental stresses
We found that miR390 was highly expressed in lateral root primordia and root tips while moderately expressed in 2-week-old seedlings and lowly expressed in other tissues (Fig. 1a)
Staining assay of the transgenic plants showed that a striking GUS activity of miR390 in the primary root tips was firstly observed after 3 days of incubation, while a weaker GUS activity of miR393 just emerged at the base of the primary root [Fig. 1b. (a) and (e)]
Summary
Plants have evolved excellent ability of flexibly regulating the growth of organs to adapt to changing environment, for example, the modulation of lateral root development in response to environmental stresses. The response of genes to phytohormone is a basic capability for plants to regulate self-growth in order to adapt to environment. Some works in Arabidopsis showed that miR393 functions in leaf and root development [13,14,15], response to stresses [7, 12, 15,16,17], embryogenic transition [18], and auxin signaling outputs [19]. Over expression of miR393 led to changes in flag leaf angle, plant height, primary root length, seed development and sensitivity to
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