Conservation of the abscission signaling peptide IDA during Angiosperm evolution: withstanding genome duplications and gain and loss of the receptors HAE/HSL2

Abstract

The peptide INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), which signals through the leucine-rich repeat receptor-like kinases HAESA (HAE) and HAESA-LIKE2 (HSL2), controls different cell separation events in Arabidopsis thaliana. We hypothesize the involvement of this signaling module in abscission processes in other plant species even though they may shed other organs than A. thaliana. As the first step toward testing this hypothesis from an evolutionarily perspective we have identified genes encoding putative orthologs of IDA and its receptors by BLAST searches of publically available protein, nucleotide and genome databases for angiosperms. Genes encoding IDA or IDA-LIKE (IDL) peptides and HSL proteins were found in all investigated species, which were selected as to represent each angiosperm order with available genomic sequences. The 12 amino acids representing the bioactive peptide in A. thaliana have virtually been unchanged throughout the evolution of the angiosperms; however, the number of IDL and HSL genes varies between different orders and species. The phylogenetic analyses suggest that IDA, HSL2, and the related HSL1 gene, were present in the species that gave rise to the angiosperms. HAE has arisen from HSL1 after a genome duplication that took place after the monocot—eudicots split. HSL1 has also independently been duplicated in the monocots, while HSL2 has been lost in gingers (Zingiberales) and grasses (Poales). IDA has been duplicated in eudicots to give rise to functionally divergent IDL peptides. We postulate that the high number of IDL homologs present in the core eudicots is a result of multiple whole genome duplications (WGD). We substantiate the involvement of IDA and HAE/HSL2 homologs in abscission by providing gene expression data of different organ separation events from various species.

Core Mechanisms Regulating Developmentally Timed and Environmentally Triggered Abscission

“…For example, HAE homologs are also up-regulated in poplar abscission zones when abscission is activated by shading leaves , and IDA homologs are induced in soybean and tomato abscission zones prior to abscission (Tucker and Yang, 2012). In fact, the active peptide from IDA is conserved in all flowering plants (Stø et al, 2015). Also, Citrus IDA3 can complement abscission deficiency in Arabidopsis ida mutant plants (Estornell et al, 2015).…”

Molecular Events Involved in Fruitlet Abscission in Litchi

“…However, whether LcIDL1 and LcHSL2 could form a ligand-receptor complex requires further investigation, which can be done primarily through an ox-burst system established by Butenko lab [60]. In fact, recent studies have shown that IDA-HAE/HSL2 signaling components were found across the plant kingdom, such as citrus, tomato, soybean, oil palm, and poplar [4,[62][63][64][65], suggesting that different cell separation processes might share the IDA-HAE/HSL2 signaling module that is conserved across plant species.…”

Advances in abscission signaling

“…Recent research indicates that the Arabidopsis abscission module likely extends far past Arabidopsis. A phylogenetic study showed that IDA is conserved in all flowering plants (Stø et al ., 2015). HAE homologs are up-regulated in Poplar leaf AZs that are abscising due to shading (Jin et al ., 2015).…”