http://omicsomics.blogspot.com/2010/02/celebrating-citrus.html

Friday, February 12, 2010

Celebrating Citrus



I've been on a citrus kick at work lately, trying out different varieties I picked up at one of the adjacent grocery stores (curiously, we're sandwiched between 2). When I was growing up I think I knew only seeded oranges, navel oranges, tangerines, tangelos, grapefruit, lemons and limes. Through some combination of better awareness and better availability, there's a lot more I can find. I gained some notoriety this week by bringing a pummelo to a breakfast meeting; if you haven't seen one, they make grapefruit look small. Tastewise, it's a bit milder and a bit sweeter than a grapefruit.

A lot of this is seasonal, as I've been finding. Kumquats are a nearly perfect desk snack -- completely neat except for the need to spit the pips -- but seem to be available only around the New Year -- and then only in a few stores. Amongst the treats currently available are clementines -- almost as good a desk snack as kumquats though you do need to peel them and some wonderful non-orange oranges. Cara cara oranges turn out to be delightfully pink on the inside whereas the blood oranges are precisely named -- after one knife slip I found myself searching my skin in vain for the source of the red spots on the table.

What I can find in the store is still just a tiny sample of all the citrus known to exist. My brother sent me a New Yorker article on professional flavorists which mentioned many more, including pummelos with quite foul-smelling rinds but yet another delicious flavor of pulp.

Just after the turn of the century, a very good review of citrus genetics was published in Trends in Genetics. The molecular story appears to point to all this wonderful diversity originating from three wild species. Amazing! It gets stranger when you delve into the reproductive biology of citrus -- not only can they be propagated sexually or by cuttings, but they are quite adept at apomixis, the development of a new individual from an unfertilized ovum.

There is, of course, a citrus genome project, hosted at the JGI. And perhaps more predictably, I'm a bit impatient for completion. As the rationale page explains (and from which I've stolen the wonderful image of citrus diversity above), the sweet orange genome is only 382 Mb. When the new HiSeq and SOLiD instruments come on-line, they could sequence several individuals at 40X coverage in one run.

What I'd really like is to have the genetic blueprint for all those wonderful flavors and colors in order to repackage them. Keeping in mind, of course, that some useful characteristics (such as seedlessness) aren't simple traits but products of karytype (I would love a fully seedless kumquat!). Imagine if you could have a whole series of clementine-like fruits, with the size & easy peeling characteristics but with the whole range of other citrus flavors and colors genetically grafted in -- cara cara clementines and blood clementines and ruby red clementines and perhaps even sweet lemontines and key clemenlimes. What a wonderfully healthy snacking then!

Posted by Keith Robison at 11:18 PM