Abstract
Fundamental processes that underpin plant growth and development depend crucially on the action and assembly of the cell wall, a dynamic structure that changes in response to both developmental and environmental cues. While much is known about cell wall structure and biosynthesis, much less is known about the functions of the individual wall components, particularly with respect to their potential roles in cellular signaling. Loss-of-function mutants of two arabinogalactan-protein (AGP)-specific galactosyltransferases namely, GALT2 and GALT5, confer pleiotropic growth and development phenotypes indicating the important contributions of carbohydrate moieties towards AGP function. Notably, galt2galt5 double mutants displayed impaired root growth and root tip swelling in response to salt, likely as a result of decreased cellulose synthesis. These mutants phenocopy a salt-overly sensitive mutant called sos5, which lacks a fasciclin-like AGP (SOS5/FLA4) as well as a fei1fei2 double mutant, which lacks two cell wall-associated leucine-rich repeat receptor-like kinases. Additionally, galt2gal5 as well as sos5 and fei2 showed reduced seed mucilage adherence. Quintuple galt2galt5sos5fei1fei2 mutants were produced and provided evidence that these genes act in a single, linear genetic pathway. Further genetic and biochemical analysis of the quintuple mutant demonstrated involvement of these genes with the interplay between cellulose biosynthesis and two plant growth regulators, ethylene and ABA, in modulating root cell wall integrity.
Highlights
Growing plant cells control the biogenesis, deposition, and remodeling of the cell wall
This paper provides support for this hypothesis by generating and functionally characterizing quintuple mutant plants along with other related genetic mutants, such as galt2galt5 double mutants and sos5fei1fei2 triple mutants
Transcriptome analyses using RNA extracted from laser-capture dissected seed coat tissue indicated that the transcript levels of GALT2, GALT5, FEI1, FEI2, and SOS5 are high in the seed coat during early embryogenesis (S2 Fig; http:// seedgenenetwork.net/arabidopsis; http://bar.utoronto.ca/efp_seedcoat/cgi-bin/efpWeb.cgi) [33], [34]
Summary
Growing plant cells control the biogenesis, deposition, and remodeling of the cell wall. Mounting evidence indicates that a dedicated plant cell wall integrity (CWI) maintenance mechanism exists in plants [2]. This mechanism monitors and maintains the functional integrity of the wall during different biological processes, including exposure to abiotic and biotic stress [3], [4]. While our understanding of the mechanisms involved in biosynthesis of cell wall polymers have increased significantly, current understanding of the components and mechanisms involved in the perception and regulation of processes maintaining CWI is limited
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