Centre for Plant Science, School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia
In plants, sucrose (Suc) is synthesised in source leaves and then translocated through the phloem to non-photosynthetic sink tissues. Upon reaching sink cells, Suc is often apoplasmically hydrolysed by cell wall invertase (CWIN) into glucose (Glc) and fructose (Fru) as building blocks, energy source and signalling molecules for growth, development and yield formation (1). Despite the central roles of CWIN in assimilate partitioning and sugar signalling, however, the upstream molecular machineries that control CWIN expression in plants remain unknown (1). This PhD project therefore aims to identify the upstream regulatory genes controlling CWIN expression in reproductive organs using Arabidopsis thaliana as a model plant. We hypothesised that CWIN gene expression is regulated by transcription factors (TFs) and small RNAs (sRNAs) at the transcriptional and post-transcriptional levels. Bioinformatics analysis was used to identify candidate regulatory genes encoding TFs or sRNAs that likely control the expression of CWIN2 and CWIN4, which are highly expressed in Arabidopsis reproductive organs (flower and silique). As a result, 18 TF genes and one microRNA (miRNA), miR3932, were selected as putative regulators of CWIN2 or CWIN4 for further validation. Among the 18 TF candidates, ARF6, ARF8, AP3 and CRC were identified as putative regulators for CWIN gene expression based on the finding that CWIN2 or CWIN4 expression was significantly reduced in arf6, arf8, ap3 and crc mutants. The miR3932, which matches CWIN2 RNA sequence, was found to be expressed in a complementary fashion with CWIN2, indicating miR3292 may be involved in mediating CWIN2 RNA degradation. In the future, a combination of molecular and biochemical approaches will be employed to further confirm the candidate regulators of CWIN2 or CWIN4, and to examine the nature of their regulation of CWIN gene expression in Arabidopsis reproductive organs. (1) Ruan Y-L 2014 Annu Rev Plant Biol 65, 33-67.