Does Small RNA Expression Affect Citrus Fruit Quality in Grafted Citrus?

Citrus is most often propagated through grafting and scion-rootstock combinations cause large effects on many fruit quality traits. Presently, the explanation for these differences has not been extensively studied at the genetic level. One potential reason for rootstock effects on fruit quality is the presence of small RNAs (sRNAs), molecules known to affect gene expression and plant development. Species-specific sRNAs have been discovered in a wide variety of plants. Many are differentially expressed and are able to cross a graft union to influence scion traits.

We hypothesize that species-specific sRNAs exist in citrus and that the abundance of sRNAs can greatly impact the quality of fruit produced. In this study, fruit and root samples were collected from sweet orange scions grafted onto 4 genetically differing rootstocks, trifoliate orange, Carrizo citrange, rough lemon, and sweet orange. Three replicate samples of each genotype were collected from a Washington navel orange rootstock trial planted in Riverside at 4 time points throughout the 2014-2015 growing season. sRNAs were sequenced to quantify their abundance in each sample. ~15% of reads sequenced matched previously known, conserved sRNAs. This leaves many reads that will be assessed as potentially novel, species-specific sRNAs. Many of the conserved sRNAs are differentially expressed between the different rootstocks. The sequencing results will be correlated to phenotypic data to identify sRNAs influencing changes in fruit quality.