The ALBA RNA-binding proteins function redundantly to promote growth and flowering in Arabidopsis.

RNA-binding proteins (RBPs) are critical regulators of gene expression, but have been poorly studied relative to other classes of gene regulators. Recently, mRNA-interactome capture identified many Arabidopsis RBPs of unknown function, including a family of ALBA domain containing proteins. Arabidopsis has three short-form ALBA homologues (ALBA1-3) and three long-form ALBA homologues (ALBA4-6), both of which are conserved throughout the plant kingdom. Despite this ancient origin, ALBA-GUS translational fusions of ALBA1, ALBA2, ALBA4, and ALBA5 had indistinguishable expression patterns, all being preferentially expressed in young, rapidly dividing tissues. Likewise, all four ALBA proteins had indistinguishable ALBA-GFP subcellular localizations in roots, all being preferentially located to the cytoplasm, consistent with being mRNA-binding. Genetic analysis demonstrated redundancy within the long-form ALBA family members; in contrast to single alba mutants that all appeared wild-type, a triple alba456 mutant had slower rosette growth and a strong delay in flowering-time. RNA-sequencing found most differentially expressed genes in alba456 were related to metabolism, not development. Additionally, changes to the alba456 transcriptome were subtle, suggesting ALBA4-6 participates in a process that does not strongly affect transcriptome composition. Together, our findings demonstrate that ALBA protein function is highly redundant, and is essential for proper growth and flowering in Arabidopsis.\n\nHighlightThe RNA-binding ALBA proteins have indistinguishable expression patterns and subcellular localizations in Arabidopsis, acting redundantly to promote growth and flowering via a mechanism that does not strongly affect transcriptome composition.