Abstract 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. Highlight The 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.

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