Expression of cytokinin, nutrient transporter and meristem identity genes during pod and seed development in Pisum sativum
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Pea was used as a model species to study the differential (spatial and temporal) expression of cytokinin regulatory genes, nutrient transporter genes and key meristem identity genes in two different pea cultivars (Bolero and Bohatyr) in order to elucidate the molecular mechanisms underpinning pod set and seed quality and quantity. Knowledge about which of these genes are expressed at high (or low) levels in specific tissues and at specific time points, will allow plant breeders to target the genes of interest in those tissues and/or developmental stages in order to maximise either seed yield or seed quality, or both. The expression patterns of genes from six different gene families were studied using RT-qPCR, including cytokinin biosynthetic genes (PsIPT), cytokinin metabolic genes (PsCKX), sucrose transporter genes (PsSUT), amino acid permease genes (PsAAP), and shoot apical meristem genes (PsWUS and PsCLV). The effect of the application of a compound called INCYDE (2-Chloro-6-(3-methoxyphenyl)aminopurine), which is known to inhibit cytokinin oxidase/dehydrogenase, was investigated to observe its effect on gene expression and on components of yield of the Bolero cultivar. Specific members of the multi-gene families of PsIPT, PsCKX, PsSUT and PsAAP, as well as PsWUS and PsCLV exhibited strong differential expression in either very early stages of development, in meristem tissues (e.g. SUT10 and WUS), seed tissues (e.g. CKX1, SUF1, AAP1 and AAP6c) or in podwall tissues (e.g. CKX2, SUT1b and AAP6d). In one replicate, following the application of INCYDE to immature flowers, expression of CKX gene family members was increased in very early stages of treated plants over controls. However, in a small glasshouse experiment, application of INCYDE had no effect on yield. Certain genes were found not to be expressed at detectable levels in the tissues examined in this project (e.g. IPT3, CKX3, SUT4 and AAP8), whereas some were constitutively expressed (e.g. IPT4, SUT2 and AAP2b), and yet other genes (e.g. CKX1, CKX2, SUF1, AAP1 and AAP6c) may serve as good targets in future work to assess for yield enhancement by either upregulation or down-regulation of their expression.