The role of HEAT SHOCK PROTEIN 70-1 in cell wall metabolism

Plants, as sessile organisms, respond to different environmental stresses by modification of plant growth. Changes in cell shape and size are obtained in part through remodeling of plant cell wall composition and structure. Mutant analysis suggests that the receptor-like kinases, FEI1 and FEI2, are required for proper cell wall deposition in different developmental contexts. The fei1fei2 double mutant display perturbation of cell wall deposition leading to short and swollen roots, wide hypocotyls of dark-grown seedlings and mal-formed seed mucilage. Genetic screen identified three independent alleles of HEAT SHOCK PROTIEN 70-1 (HSP70-1) as suppressors of fei1fei2. These alleles, named hsp70-1^shou5, suppress the fei1fei2 phenotype in all developmental contexts. In addition, the hsp70-1^shou5-1 allele suppresses salt overly sensitive 5 (sos5) as well. HSP70s are highly conserved ATP-driven chaperones encoded by enlarged gene families in Arabidopsis. To analyze the effect of the hsp70-1^shou5 mutations on cell wall composition and structure, seed mucilage of the different genotypes was analyzed using monosaccharide analysis and immuno-labeling. Mucilage monosaccharide composition analysis unravel that the hsp70-1^shou5 mutation recovers the levels of the rhamnogalacturonan I (RGI) components, rhamnose and galacturonic acid, in the adherent mucilage fraction. Similar results can be observed also with regard to xylan and additional minor components of the mucilage. These results are in line with the recovery in seed mucilage cellulosic-ray formation observed using pontamine stain and immuno-labeling with the AX1 anti-xylan antibody. Altogether these results suggest the hsp70-1^shou5 alleles affect cell wall composition and the complex interaction network between cell wall polysaccharides.