Filling the Gap: Functional Clustering of ABC Proteins for the Investigation of Hormonal Transport in planta

Abstract

Plant hormones regulate a myriad of plant processes, from seed germination to reproduction, from complex organ development to microelement uptake. Much has been discovered on the factors regulating the activity of phytohormones, yet there are gaps in knowledge about their metabolism, signaling as well as transport. In this review we analyze the potential of the characterized phytohormonal transporters belonging to the ATP-Binding Cassette family (ABC proteins), thus to identify new candidate orthologs in model plants and species important for human health and food production. Previous attempts with phylogenetic analyses on transporters belonging to the ABC family suggested that sequence homology per se is not a powerful tool for functional characterization. However, we show here that sequence homology might indeed support functional conservation of characterized members of different classes of ABC proteins in several plant species, e.g., in the case of ABC class G transporters of strigolactones and ABC class B transporters of auxinic compounds. Also for the low-affinity, vacuolar abscisic acid (ABA) transporters belonging to the ABCC class we show that localization-, rather than functional-clustering occurs, possibly because of sequence conservation for targeting the tonoplast. The ABC proteins involved in pathogen defense are phylogenetically neighboring despite the different substrate identities, suggesting that sequence conservation might play a role in their activation/induction after pathogen attack. Last but not least, in case of the multiple lipid transporters belong to different ABC classes, we focused on ABC class D proteins, reported to transport/affect the synthesis of hormonal precursors. Based on these results, we propose that phylogenetic approaches followed by transport bioassays and in vivo investigations might accelerate the discovery of new hormonal transport routes and allow the designing of transgenic and genome editing approaches, aimed to improve our knowledge on plant development, plant–microbe symbioses, plant nutrient uptake and plant stress resistance.

Root-Secreted Coumarins and the Microbiota Interact to Improve Iron Nutrition in Arabidopsis

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How Machine Learning Methods Helped Find Putative Rye Wax Genes Among GBS Data

“…The ABCG is the largest one among eight (A-I) plant subfamilies [ 40 , 81 ]. Particular classes of multiple ABC transporters participate in the transport of different lipids, including FAs, waxes, and sterols [ 82 ].…”

Role of transporters in plant disease resistance

“…The ABC transporters belong to a well‐studied transporter family present ubiquitously with many members. Furthermore, the transport of defense‐related secondary metabolites is mainly executed by the G and B subfamilies of the ABC transporters family (ABCG and ABCB; Hwang et al, 2016, Borghi et al, 2019). Members of the NRAMP family belong to the amino acid‐polyamine‐organocation (APC) superfamily of secondary carrier proteins and are involved in the transport of divalent metal cations such as Fe 2+ , Mn 2+ , Zn 2+ , and Cd 2+ , and some trivalent ions (Bozzi et al, 2016).…”