Chapter 17, Problem 37P

Persimmons (Diospyros lotus) are dioecious plants, meaning that male (XY) and female (XX) flowers exist on separate plants. Male persimmon flowers have rudimentary, nonfunctional carpels (the female sex organ that includes the ovary), while female flowers have stamens and anthers (male sex organs), but no pollen is produced. Remarkably, sex determination in D. lotus is controlled by a Y-linked miRNA gene called OGI (male tree in Japanese), whose target mRNA is encoded by an autosomal gene called MeGI (female tree).

a.	What features of the OGI transcript base sequence might have suggested to the investigators that OGI encodes a miRNA?
b.	RNA-Seq experiments detected high levels of MeGI mRNA in female sex organs but low levels in male sex organs. Suggest a molecular mechanism by which the OGI miRNA could regulate MeGI gene expression.
	Integrating transgenes into the D. lotus genome is difficult. Therefore, to examine the function of MeGI, the scientists constructed a transgene that overexpresses MeGI and used it to transform Arabidopsis thaliana, a plant species more amenable to such studies. Arabidiposis have so-called perfect flowers—individual flowers have both male and female structures. MeGI overexpression in the transformants sterilized the anthers, but the carpels were unaffected and functional.
c.	What do you predict would happen if the Arabidopsis transformants also contained a transgene that overexpressed OGI?
d.	The MeGI protein is a homeobox transcription factor. What do the results with transformed Arabidopsis suggest is one role of this protein in persimmon sex determination?
e.	Speculate about possible mechanisms that could account for the rudimentary development of the nonfunctional carpels in male persimmon flowers. Could any of these mechanisms involve OGI and MeGI?