Sequence and functional analysis of MIR319 promoter homologs from Brassica juncea reveals regulatory diversification and altered expression under stress

MIR159 regulates multiple aspects of stamen and carpel development and requires dissection and delimitation of differential downstream regulatory network for manipulating fertility traits

Unravelling genetic networks regulating developmental programs are key to devising and implementing genomics assisted trait modification strategies. It is crucial to understand the role of small RNAs, and the basis of their ability to modify traits. MIR159 has been previously reported to cause defects in anther development in Arabidopsis; however, the complete spectrum and basis of the defects remained unclear. The present study was therefore undertaken to comprehensively investigate the role of miR159 from Brassica juncea in modulating vegetative and reproductive traits. Owing to the polyploid nature of Brassica, paralogous and homeologous copies of MIR159A, MIR159B, and, MIR159C were identified and analysis of the precursor uncovered extensive structural and sequence variation. The MIR159 locus with mature miR159 with perfect target complimentarily with MYB65, was cloned from Brassica juncea var. Varuna for functional characterization by generating constitutively over-expressing lines in Arabidopsis thaliana Col-0. Apart from statistically significant difference in multiple vegetative traits, drastic differences were observed in stamen and pistil. Over-expression of miR159a led to shortening of filament length and loss of tetradynamous condition. Anthers were apiculate, with improper lobe formation, and unsynchronized cellular growth between connective tissue and another lobe development. Analysis revealed arrested meiosis/cytokinesis in microspores, and altered lignin deposition pattern in endothecial walls thus affecting anther dehiscence. In the gynoecium, flaccid, dry stigmatic papillae, and large embryo sac in the female gametophyte was observed. Over-expression of miR159a thus severely affected pollination and seed-set. Analysis of the transcriptome data revealed components of regulatory networks of anther and carpel developmental pathway, and lignin metabolism that are affected. Expression analysis allowed us to position the miR159a-MYB65 module in the genetic network of stamen development, involved in pollen-grain maturation; in GA-mediated regulation of stamen development, and in lignin metabolism. The study, on one hand indicates role of miR159a-MYB65 in regulating multiple aspects of reproductive organ development that can be manipulated for trait modification, but also raises several unaddressed questions such as relationship between miR159a and male-meiosis, miR159a and filament elongation for future investigations. Accession numbers: KC204951-KC204960. Project number PRJNA1035268.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01377-7.

Combined Stress Conditions in Melon Induce Non-additive Effects in the Core miRNA Regulatory Network

Climate change has been associated with a higher incidence of combined adverse environmental conditions that can promote a significant decrease in crop productivity. However, knowledge on how a combination of stresses might affect plant development is still scarce. MicroRNAs (miRNAs) have been proposed as potential targets for improving crop productivity. Here, we have combined deep-sequencing, computational characterization of responsive miRNAs and validation of their regulatory role in a comprehensive analysis of response of melon to several combinations of four stresses (cold, salinity, short day, and infection with a fungus). Twenty-two miRNA families responding to double and/or triple stresses were identified. The regulatory role of the differentially expressed miRNAs was validated by quantitative measurements of the expression of the corresponding target genes. A high proportion (ca. 60%) of these families (mainly highly conserved miRNAs targeting transcription factors) showed a non-additive response to multiple stresses in comparison with that observed under each one of the stresses individually. Among those miRNAs showing non-additive response to stress combinations, most interactions were negative, suggesting the existence of functional convergence in the miRNA-mediated response to combined stresses. Taken together, our results provide compelling pieces of evidence that the response to combined stresses cannot be easily predicted from the study individual stresses.