SHORT INTEGUMENTS 2 promotes growth during Arabidopsis reproductive development.

The short integuments 2 (sin2) mutation arrests cell division during integument development of the Arabidopsis ovule and also has subtle pleiotropic effects on both sepal and pistil morphology. Genetic interactions between sin2 and other ovule mutations show that cell division, directionality of growth, and cell expansion represent at least partially independent processes during integument development. Double-mutant analyses also reveal that SIN2 shares functional redundancy with HUELLENLOS in ovule primordium outgrowth and proximal-distal patterning and with TSO1 in promotion of normal morphological development of the four whorls of primary floral organs. All of these observations are consistent with SIN2 being a promoter of growth and cell division during reproductive development, with a primary role in these processes during integument development. On the basis of the floral pleiotropic effects observed in a majority of ovule mutants, including sin2, we postulate a relationship between ovule genes and the evolutionary origin of some processes regulating flower morphology.