Abstract
Phase change from vegetative to reproductive development is one of the critical developmental steps in plants, and it is regulated by both environmental and endogenous factors. The maintenance of shoot apical meristem (SAM) identity, miRNAs and flowering integrators are involved in this phase change process. Here, we report that the miRNA osa-miR171c targets four GRAS (GAI-RGA-SCR) plant-specific transcription factors (OsHAM1, OsHAM2, OsHAM3, and OsHAM4) to control the floral transition and maintenance of SAM indeterminacy in rice (Oryza sativa). We characterized a rice T-DNA insertion delayed heading (dh) mutant, where the expression of OsMIR171c gene is up-regulated. This mutant showed pleiotropic phenotypic defects, including especially prolonged vegetative phase, delayed heading date, and bigger shoot apex. Parallel expression analysis showed that osa-miR171c controlled the expression change of four OsHAMs in the shoot apex during floral transition, and responded to light. In the dh mutant, the expression of the juvenile-adult phase change negative regulator osa-miR156 was up-regulated, expression of the flowering integrators Hd3a and RFT1 was inhibited, and expression of FON4 negative regulators involved in the maintenance of SAM indeterminacy was also inhibited. From these data, we propose that the inhibition of osa-miR171c-mediated OsHAM transcription factors regulates the phase transition from vegetative to reproductive development by maintaining SAM indeterminacy and inhibiting flowering integrators.
Highlights
MicroRNAs regulate gene expression by sequence-specific cleavage or translational repression of cognate mRNAs in plants and animals [1,2]
The time required between sowing and heading was at least twice as long as the timing exhibited by the wild-type Zhonghua11 (ZH11) (Fig 1B)
We identified that four OsHAMs transcripts are cleaved under direction of osa-miR171c in rice (Fig 2B and 2C), and the up-regulation of osa-miR171c resulted in prolonged vegetative phase and serious delayed rice heading date
Summary
MicroRNAs (miRNAs) regulate gene expression by sequence-specific cleavage or translational repression of cognate mRNAs in plants and animals [1,2]. During post-embryonic life, juvenile—adult transition ( known as the vegetative phase change) and vegetative—reproductive transition represent the two main developmental transitions [10] These transitions are important, firstly, plants can enter a reproductive stage under appropriate environmental conditions only during the adult phase [10]; the juvenile —adult phase change plays a critical role in plant development. In rice, this phase transition is usually associated with a series of changes in a range of species-specific traits, including the presence of a mid-rib, size and shape of the leaf blades, shoot apical meristem (SAM) size, and photosynthetic rate, etc [11]. Recent studies in both maize and rice have suggested that the WUS-CLV feedback loop pathway is conserved in grasses [28,29,30]
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