Disruption of OsEXO70A1 Causes Irregular Vascular Bundles and Perturbs Mineral Nutrient Assimilation in Rice

Abstract

Normal uptake, transportation, and assimilation of primary nutrients are essential to plant growth. Tracheary elements (TEs) are tissues responsible for the transport of water and minerals and characterized by patterned secondary cell wall (SCW) thickening. Exocysts are involved in the regulation of SCW deposition by mediating the targeted transport of materials and enzymes to specific membrane areas. EXO70s are highly duplicated in plants and provide exocysts with functional specificity. In this study, we report the isolation of a rice mutant rapid leaf senescence2 (rls2) that exhibits dwarfism, ferruginous spotted necrotic leaves, decreased hydraulic transport, and disordered primary nutrient assimilation. Histological analysis of rls2-1 mutants has indicated impaired cell expansion, collapsed vascular tissues, and irregular SCW deposition. Map-based cloning has revealed that RLS2 encodes OsEXO70A1, which is one of the 47 members of EXO70s in rice. RLS2 was widely expressed and spatially restricted in vascular bundles. Subcellular localization analysis demonstrated that RLS2 was present on both membrane and nuclear regions. Expression analysis revealed that mutations in rls2 triggers transcriptional fluctuation of orthologous EXO70 genes and affects genes involved in primary nutrient absorption and transport. In brief, our study revealed that RLS2 is required for normal vascular bundle differentiation and primary nutrient assimilation.

The Physcomitrella patens exocyst subunit EXO70.3d has distinct roles in growth and development, and is essential for completion of the moss life cycle

“…Yet another EXO70.2 subfamily proliferated in conifers, and even in mosses EXO70.2 is the clade with the most paralogs. The extent of within-clade divergence varies among the three families, with EXO70.1 being the least diverged, possibly due to strong purifying selection, consistent with the severe phenotypic consequences of loss of highly expressed EXO70.1 paralogs in A. thaliana (Synek et al, 2006;Li et al, 2013) and rice (Tu et al, 2015). Most experimental work on plant EXO70 reported so far has concentrated on EXO70.1 and EXO70.2, except one study describing the role of a Medicago truncatula EXO70.3 in mycorrhiza (Zhang et al, 2015).…”

Microtubule‐dependent targeting of the exocyst complex is necessary for xylem development in Arabidopsis

“…However, we show that secondary CESAs, represented by CESA7, which are responsible for cellulose synthesis in TEs, have differentially disturbed localization in exocyst mutants – from only partial mislocalization to the fully delocalized signal, or even possibly released from the PM. These findings are in full agreement with a recent study, in which the authors described large deviations in xylem cell wall biogenesis in OsEXO70A1 rice mutant plants – collapsed vascular tissues and irregular SCW deposition (Tu et al ., ). It is possible that CESA mislocalization in exocyst mutants is a consequence of perturbations in cell wall or PM composition as a result of the lack of functional exocyst complex, and that CESAs are not a direct cargo for exocyst‐mediated secretion.…”

“…In the most recent study, Tu et al . () showed the importance of functional OsEXO70A1 for TE development in rice.…”

“…Derbyshire et al (2015) identified several exocyst subunits in MT pull-downs on extracts from TEs in Arabidopsis suspension cultures. In the most recent study, Tu et al (2015) showed the importance of functional OsEXO70A1 for TE development in rice.…”

OsExo70B1 Positively Regulates Disease Resistance to Magnaporthe oryzae in Rice

“…Among them, Exo70 is a key member of the exocyst complex and has been found to be widely present in yeast, mammals and plants [ 13 , 14 ]. In yeast and mammals, there is one Exo70 gene, while there are multiple copies of Exo70 genes in plants [ 15 ] ranging from 21 to 47 Exo70 members in potatoes, Arabidopsis, Populus trichocarpa, wheat and rice [ 16 , 17 , 18 , 19 , 20 ]. Exo70 genes have been duplicated independently in the moss, lycophyte and angiosperm lineages, and in the subsequent lineage-specific multiplications which are represented by nine subgroups (Exo70A–Exo70I) [ 15 ] and their function ranges from growth, development to biotic and abiotic stresses [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ].…”