Pospiviroid Infection of Tomato Regulates the Expression of Genes Involved in Flower and Fruit Development.

Viroids are unencapsidated, single-stranded, covalently-closed circular, highly structured, noncoding RNAs of 239⁻401 nucleotides that cause disease in several economically important crop plants. In tomato ( cv. Rutgers), symptoms of pospiviroid infection include stunting, reduced vigor, flower abortion, and reduced size and number of fruits, resulting in significant crop losses. Dramatic alterations in plant development triggered by viroid infection are the result of differential gene expression; in our study, we focused on the effect of tomato planta macho viroid (TPMVd) and Mexican papita viroid (MPVd) infection on gene networks associated with the regulation of flower and fruit development. The expression of several of the genes were previously reported to be affected by viroid infection, but two genes not previously studied were included. Changes in gene expression of (bHLH transcription factor) and (proline-like tRNA synthetase) are involved in petal morphology and fertility, respectively. Expression of was down-regulated in flowers of TPMVd- and MPVd-infected plants, while expression of was up-regulated in flowers. Up-regulation of and down-regulation of were positively correlated with symptoms such as reduced petal size and flower abortion. Expression analysis of additional tomato genes and a prediction of a global network association of genes involved in flower and fruit development and impacted by viroid infection may further elucidate the pathways underlying viroid pathogenicity.