The role of organ - and daylength - specific gene expression in bulb development and resource management in onion (ALLIUM CEPA L.)

Abstract

Onion development is a complex process with each developmental event depending on the adequate supply of resources. Also, these resource components themselves are crucial nutrients in onion when consumed as food. For higher yield and better quality in onion production, it is essential to not only have a high level of photosynthesis but also effective transportation of photosynthetic products. A comprehensive set of spatial and developmental time-course experiments detailed the gene expression in onion leaf and bulb tissues during the development of a long-day onion cultivar under long-day and short-day conditions. Candidates included well characterised functional clock genes in Arabidopsis flowering pathway, as well as some novel sequences differentially expressed in bulb tissues. Both AcFT1 and AcFT4 showed significant increasing expression level during plant development, with AcFT1 being expressed in long-days during bulb formation and AcFT4 in short-days where bulbs are not formed. The data further support the role of AcFT1 as a promoter and AcFT4 as inhibitor in onion bulb formation. A number of genes associated with onion carbohydrate metabolism, sulphur metabolism and bulb development were identified as having different tissue-specific expression and provide targets for future studies.