M O I L A B - 2020 02 21 Commentary PNAS

(unrolled thread https://threadreaderapp.com/thread/1232193521659998209.html)

tl;dr of our short @PNASNews synthesis on adaptive timings in A. thaliana. How do they know when to germinate or flower in seasonal climates? (Spoiler alert: more complicated than winter and spring cycles!)

dx.doi.org/10.1073/pnas.1…

@carnegiescience @CarnegiePlants @Stanford

👇

The classic observation that some ecotypes needed a cold treatment to flower when grown in cozy-warm laboratory conditions suggested two life modes: populations that time their germination to fall and flower in spring after the cold winter (winter cyclers/annuals),

and populations that germinate in spring/summer and flower without ever experiencing cold (spring cyclers/annuals).

Although the winter vs spring annual simplification was a useful, it was just deduced from half of the puzzle: when they flower; and everybody acknowledged things are more complex than that (hint: germination?)

[Parenthesis: flowering time control is pretty cool (see rev. https://dx.doi.org/10.1242/dev.01294). A key master transcription regulator that represses flowering is FLC. As cold days accumulate, this gene itself is downregulated as it accumulates DNA methylations and histone modifications!]

So what about when to germinate? That is the other key half of the puzzle to seasonal life timing. It has long been known that seeds also have "germination blocks" that respond to the environment, but not until recently (Martinez-Berdeja PNAS https://dx.doi.org/10.1073/pnas.1912451117 ) a really large collection of >500 genotypes was studied in detail for their germination. These belong to the 1001G (dx.doi.org/10.1016/j.cell…) so they had a better representation of older Mediterranean lineages and could map the variation in germination along the genome.

Both temperature-responsive and temperature-independent germination was controlled by the gene DOG1. [Parenthesis: although of unknown exact function, DOG1 protein product cycles with climate https://dx.doi.org/10.1073/pnas.1116325108!]

Mapping the new dimension of germination with flowering across the geographic range of Arabidopsis, the life timing behaviors can be summarized in 4: (1) coastal hot Mediterranean populations, with low germination and rapid growth during mild winter (Huelva, Spain)

(2) montane Mediterranean populations, which germinate before cold periods and more rigorously sense cold before flowering (but their cycle seems quite flexible) (Valdepeñas, Spain)

(3) Central European weedy populations, which grow fast and were domesticated as a laboratory strain (like Col-0). This is the canonical "spring/summer cycler" (Tuebingen, Germany)

(4) Scandinavian slow growers and late bloomers, which germinate early but spend quite some of their lives under the snow to flower in spring. (Skane, Sweden)

Excited about all we are learning regarding climate adaptation and its genetic basis from what otherwise was considered the plant laboratory rat -- looking forward to many more discoveries ahead!

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