PpLEA genes in embryophytes,instead of LEAs being angiosperm-unique

Abstract

From the earliest land plants (Bryophyta) to the highly diversified flowering plants (Angiosperm), late embryogenesis abundant (LEA) genes/proteins are consistently identified across embryophytes. LEA proteins are intrinsically disordered proteins that are spatiotemporally expressed in floral organs/fruits or specifically somatic embryogenesis among various cell types. Moreover, LEA genes are typically responsive to various environmental stressors. To disclose the multifaceted features from vegetative to productive processes, this mini-review summarizes current knowledge on PpLEA genes/proteins in Physcomitrella patens (P. patens)-- a representative ancestral bryophyte land plant. In P. patens, LEA proteins maintain basal expression levels in protonema, probably due to the sufficient water supply under normal growth conditions; comparably those proteins are significantly accumulated in mature gametophores, consistent with a dehydration-protective function, revealing their extensive roles throughout development progression. While a majority of PpLEA genes consistently expressed across gametophyte-to-sporophyte transition, indicating their putative role linking vegetative and reproductive development. Only one single PpLEA gene showing differential transcriptional expression during the gametophyte to sporophyte transition is activated at this developmental onset and maintains the expression thereafter, suggesting its unique and non-redundant function linking vegetative and reproductive developmental stages. In addition, P. patens biosynthesize distinct LEA proteins in response to drought, chilling or abscisic acid (ABA) and the other abiotic stimulus. Therefore, the roles of PpLEAs can be further exploited in multifaceted ways. These findings shed light on the linkage between abiotic stress responses and plant development processes, particularly the transition from vegetative growth to reproductive development.