SHI family transcription factors regulate an interspecific barrier

Pre-zygotic interspecies incompatibility in angiosperms is an important mechanism to prevent unfavourable hybrids between species. Here we report our identification of STIGMATIC PRIVACY 2 (SPRI2), a transcription factor that has a zinc-finger domain and regulates interspecies barriers in Arabidopsis thaliana, via genome-wide association study. Knockout analysis of SPRI2/SRS7 and its paralogue SPRI2-like/SRS5 demonstrated their necessity in rejecting male pollen from other species within female pistils. Additionally, they govern mRNA transcription of xylan O-acetyltransferases (TBL45 and TBL40) related to cell wall modification, alongside SPRI1, a pivotal transmembrane protein for interspecific pollen rejection. SPRI2/SRS7 is localized as condensed structures in the nucleus formed via liquid-liquid phase separation (LLPS), and a prion-like sequence in its amino-terminal region was found to be responsible for the formation of the condensates. The LLPS-regulated SPRI2/SRS7 discovered in this study may contribute to the establishment of interspecific reproductive barriers through the transcriptional regulation of cell wall modification genes and SPRI1.

A stigmatic gene confers interspecies incompatibility in the Brassicaceae

Pre-zygotic interspecies incompatibility in angiosperms is a male-female relationship that inhibits the formation of hybrids between two species. Here, we report on the identification of STIGMATIC PRIVACY 1 (SPRI1), an interspecies barrier gene in Arabidopsis thaliana. We show that the rejection activity of this stigma-specific plasma membrane protein is effective against distantly related Brassicaceae pollen tubes and is independent of self-incompatibility. Point-mutation experiments and functional tests of synthesized hypothetical ancestral forms of SPRI1 suggest evolutionary decay of SPRI1-controlled interspecies incompatibility in self-compatible A. thaliana. Hetero-pollination experiments indicate that SPRI1 ensures intraspecific fertilization in the pistil when pollen from other species are present. Our study supports the idea that SPRI1 functions as a barrier mechanism that permits entrance of pollen with an intrinsic signal from self species.

Molecular cloning, subcellular localization and characterization of two adenylate kinases from cassava, Manihot esculenta Crantz cv. KU50

Adenylate kinase (ADK) is a phosphotransferase that plays an important role in cellular energy homeostasis. Many isozymes located in different subcellular compartments have been reported. In this study, we focus on the characterization of cassava (Manihot esculenta) ADKs. We found 15 ADKs that are publicly available in the African cassava genome database. We cloned two ADKs, namely MeADK1 and MeADK2, which are phylogenetically grouped together with the plastidial ADK in potato. Both MeADK1 and MeADK2 showed 66% identity in the amino acid sequences with plastidial ADK in potato. However, we demonstrated that they are localized to mitochondria using GFP fusions of MeADK1 and MeADK2. The Escherichia coli-produced recombinant MeADK1 and MeADK2 preferred forward reactions that produce ATP. They exhibited similar specific activities. The semi-quantitative RT-PCR analysis showed that MeADK1 and MeADK2 in 2-month-old leaves have similar expression patterns under a diurnal light-dark cycle. However, MeADK2 transcripts were expressed at much higher levels than MeADK1 in 5-month-old leaves and roots. Thus, we conclude that MeADK2 might play a vital role in energy homeostasis in cassava mitochondria.