The AFL subfamily of B3 transcription factors: evolution and function in angiosperm seeds

Abstract

Seed development follows zygotic embryogenesis; during the maturation phase reserves accumulate and desiccation tolerance is acquired. This is tightly regulated at the transcriptional level and the AFL (ABI3/FUS3/LEC2) subfamily of B3 transcription factors (TFs) play a central role. They alter hormone biosynthesis, mainly in regards to abscisic acid and gibberellins, and also regulate the expression of other TFs and/or modulate their downstream activity via protein-protein interactions. This review deals with the origin of AFL TFs, which can be traced back to non-vascular plants such as Physcomitrella patens and achieves foremost expansion in the angiosperms. In green algae, like the unicellular Chlamydomonas reinhardtii or the pluricellular Klebsormidium flaccidum, a single B3 gene and four B3 paralogous genes are annotated, respectively. However, none of them present with the structural features of the AFL subfamily, with the exception of the B3 DNA-binding domain. Phylogenetic analysis groups the AFL TFs into four Major Clusters of Ortologous Genes (MCOGs). The origin and function of these genes is discussed in view of their expression patterns and in the context of major regulatory interactions in seeds of monocotyledonous and dicotyledonous species.

The SnRK1 Kinase as Central Mediator of Energy Signaling between Different Organelles

“…This AKIN10-dependent degradation of WRI1 provides a homeostatic mechanism that favors lipid biosynthesis when intracellular sugar levels are elevated and AKIN10 is inhibited. FUS3, a member of the AFL (ABI3/FUS3/LEC2) subfamily of B3 TFs, is a master regulator of seed maturation and hormonal responses during late embryogenesis and germination (Carbonero et al, 2017). AKIN10 was identified as a FUS3-interacting protein, and it was reported that AKIN10 physically interacts with and phosphorylates FUS3 at its N-terminal region, which delays degradation of FUS3 (Tsai and Gazzarrini, 2012).…”

Seed biology – from lab to field

“…The control of seed maturation is covered by both Leprince et al (2017) and Carbonero et al (2017), who both describe the role of ABA signalling in the control of seed metabolism, reserve accumulation and desiccation tolerance. After dealing with seed development and dormancy induction, four contributions focus on the control of dormancy and/or germination post-shedding.…”

Evolutionary Analysis of the LAFL Genes Involved in the Land Plant Seed Maturation Program

“…Among them, the AFL family of B3 transcription factors (TFs) and the LEC1 -type of NF-YB TFs, which together form LAFL regulatory network, are considered to play key roles in seed maturation. Although there were studies on the evolution of LEC1 -type genes (Xie et al, 2008), AFL genes (Li et al, 2010; Carbonero et al, 2016), this study presents a comprehensive analysis of LAFL genes by integrating their phylogeny, gene structure, cis -elements and expression patterns together for a better understanding of the evolution of seed maturation programs during plant evolution.…”

“…During the review of this manuscript, Carbonero et al (2016) published their work on the AFL family. In agreement with our results, they suggest that the origin of the AFL family traces back to a common ancestor of bryophytes and vascular plants, and that this family has expanded in the angiosperms.…”

“…However, due to different sampling regimes and sequence coverage, there are some different results between these two studies, especially relating to the evolution of LEC2 genes. According to Carbonero et al (2016), seven LEC2 genes were described from three monocots, Oryza sativa, Brachypodium distachyon and Hordeum vulgare (all grasses), but the relationship of those seven genes with other AFL homologs needs to be verified; differences in gene structure, phylogenetic position, and expression pattern suggests that these may not be LEC2 genes.…”