Abstract
Seed size is the result of complex molecular networks controlling the development of the seed coat (of maternal origin) and the two fertilization products, the embryo and the endosperm. In this study we characterized the role of Arabidopsis thaliana MADS-domain transcription factor SEEDSTICK (STK) in seed size control. STK is known to regulate the differentiation of the seed coat as well as the structural and mechanical properties of cell walls in developing seeds. In particular, we further characterized stk mutant seeds. Genetic evidence (reciprocal crosses) of the inheritance of the small-seed phenotype, together with the provided analysis of cell division activity (flow cytometry), demonstrate that STK acts in the earlier phases of seed development as a maternal activator of growth. Moreover, we describe a molecular mechanism underlying this activity by reporting how STK positively regulates cell cycle progression via directly activating the expression of E2Fa, a key regulator of the cell cycle. Altogether, our results unveil a new genetic network active in the maternal control of seed size in Arabidopsis.
Highlights
In spermatophyte plants, reproductive success depends on the ability to produce healthy seeds
In Arabidopsis, seed size is established around four days after fertilization (DAF), when the dimension of the seed cavity has reached its maximum expansion as a result of seed coat growth and endosperm proliferation [10,11]
We focused on E2Fa, a crucial transcription factor that regulates the mitotic activity of cells that is co-expressed with STK in the seed coat of developing seeds [22,23,24]
Summary
Reproductive success depends on the ability to produce healthy seeds. Seed size represents one of the major traits that influence the fitness of the plant generation. Despite their importance, molecular regulators of seed size have only begun to be identified in the last few years, mainly through studies on Arabidopsis [1,2,3,4]. The final size of Arabidopsis seeds is achieved through coordinated growth of the three parts that compose the seeds: the seed coat, the endosperm and the embryo [9]. In Arabidopsis, seed size is established around four days after fertilization (DAF), when the dimension of the seed cavity has reached its maximum expansion as a result of seed coat growth and endosperm proliferation [10,11]
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