The superwoman1-cleistogamy2 mutant is a novel resource for gene containment in rice.

Outcrossing between cultivated plants and their related wild species may result in the loss of favourable agricultural traits in the progeny or escape of transgenes in the environment. Outcrossing can be physically prevented by using cleistogamous (i.e. closed-flower) plants. In rice, flower opening is dependent on the mechanical action of fleshy organs called lodicules, which are generally regarded as the grass petal equivalents. Lodicule identity and development are specified by the action of protein complexes involving the SPW1 and OsMADS2 transcription factors. In the superwoman1-cleistogamy1 (spw1-cls1) mutant, SPW1 is impaired for heterodimerization with OsMADS2 and consequently spw1-cls1 shows thin, ineffective lodicules. However, low temperatures help stabilise the mutated SPW1/OsMADS2 heterodimer and lodicule development is restored when spw1-cls1 is grown in a cold environment, resulting in the loss of the cleistogamous phenotype. To identify a novel, temperature-stable cleistogamous allele of SPW1, targeted and random mutations were introduced into the SPW1 sequence and their effects over SPW1/OsMADS2 dimer formation were assessed in yeast two-hybrid experiments. In parallel, a novel cleistogamous allele of SPW1 called spw1-cls2 was isolated from a forward genetic screen. In spw1-cls2, a mutation leading to a change of an amino acid involved in DNA binding by the transcription factor was identified. Fertility of spw1-cls2 is somewhat decreased under low temperatures but unlike for spw1-cls1, the cleistogamous phenotype is maintained, making the line a safer and valuable genetic resource for gene containment.

Unequal genetic redundancy of rice PISTILLATA orthologs, OsMADS2 and OsMADS4, in lodicule and stamen development.

Two homologs of PISTILLATA have been identified in rice: OsMADS2 and OsMADS4. However, their roles in floral organ development are controversial. Here, we demonstrate that the genes show unequal redundancy of class B function. Although OsMADS2 plays an important role in lodicule development, OsMADS4 also supports the specification of lodicule identity. In contrast, the genes are roughly equally important in stamen development. Consistent with their redundant functions, both OsMADS2 and OsMADS4 interact with the unique rice AP3 ortholog SPW1.

SHA1, a novel RING finger protein, functions in shoot apical meristem maintenance in Arabidopsis.

Post-embryonic plant growth is dependent on a functional shoot apical meristem (SAM) that provides cells for continuous development of new aerial organs. However, how the SAM is dynamically maintained during vegetative development remains largely unclear. We report here the characterization of a new SAM maintenance mutant, sha1-1 (shoot apical meristem arrest 1-1), that shows a primary SAM-deficient phenotype at the adult stage. The SHA1 gene encodes a novel RING finger protein, and is expressed most intensely in the shoot apex. We show that, in the sha1-1 mutant, the primary SAM develops normally during the juvenile vegetative stage, but cell layer structure becomes disorganized after entering the adult vegetative stage, resulting in a dysfunctional SAM that cannot initiate floral primordia. The sha1-1 SAM terminates completely at the stage when the wild-type begins to bolt, producing adult plants with a primary inflorescence-deficient phenotype. These observations indicate that SHA1, a putative E3 ligase, is required for post-embryonic SAM maintenance by controlling proper cellular organization.