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Abstract: The GENOMESUNCOUPLED1 (GUN1) gene has been reported to encode a chloroplast-localized pentatricopeptide-repeat protein, which acts to integrate multiple indicators of plastid developmental stage and altered plastid function, as part of chloroplast-to-nucleus retrograde communication. However, the molecular mechanisms underlying signal integration by GUN1 have remained elusive, up until the recent identification of a set of GUN1-interacting proteins, by co-immunoprecipitation and mass-spectrometric analyses, as well as protein–protein interaction assays. Here, we review the molecular functions of the different GUN1 partners and propose a major role for GUN1 as coordinator of chloroplast translation, protein import, and protein degradation. This regulatory role is implemented through proteins that, in most cases, are part of multimeric protein complexes and whose precise functions vary depending on their association states. Within this framework, GUN1 may act as a platform to promote specific functions by bringing the interacting enzymes into close proximity with their substrates, or may inhibit processes by sequestering particular pools of specific interactors. Furthermore, the interactions of GUN1 with enzymes of the tetrapyrrole biosynthesis (TPB) pathway support the involvement of tetrapyrroles as signaling molecules in retrograde communication. [mehr]

What makes some clades produce more species than others? The answers may be genetic, genomic, or morphological. This talk will focus on the grass tribe Andropogoneae, an economically and ecologically important group that includes maize, sugarcane, sorghum and Miscanthus. Most species in the clade are polyploid, and we find that allopolyploidy is a predominant mode of speciation in the group. However, the net speciation rate does not increase after polyploidy. The parental genomes of most Andropogoneae polyploids diverged in the Late Miocene coincident with the expansion of the major C4 grasslands that dominate the earth today. Morphological characteristics include a distinctive seed dispersal unit derived from a pair of spikelets and the associated inflorescence stalk. This structure is usually assumed to be selected for seed dispersal, but also affects breeding system and the investment into pollen and ovules, and is a source of carbon for the developing grain. Thus the structure of the inflorescence may be under selection for pollination, seed filling, or seed dispersal. This may be as important as repeated allopolyploidy in driving speciation. [mehr]