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Description:
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Light is a very important factor affecting every aspect of plant development .
Plant developmental responses to light are sensitive to the direction , intensity , color , and
duration of light . Light is perceived by an extensive set of photoreceptors that includes
the red /far -red light–absorbing phytochromes and blue /UV -A light–absorbing
cryptochromes . The Arabidopsis mutant seedling hyper -responsive to light 6 (shl6 ) has
exaggerated developmental responses to available light . In the low light , shl6 seedlings
have a phenotype similar to wild -type plants grown in high light , with short hypocotyls ,
expanded cotyledons , and well -developed first true leaves . In addition , the roots of shl6
are short and highly branched . The SHL6 gene was mapped to a position on chromosome
5 between simple sequence length polymorphism (SSLP ) markers nga249 and nga151 .
Two cosmid clones from this interval (introduced by Agrobacterium -mediated
transformation ) complemented the shl6 mutant phenotype . One candidate gene identified
by complementation is a member of the glycosyltransferase family . The sequence of shl6
mutant differs from wild type Columbia allele of this gene (At5g13000 ) by a single
nucleotide substitution in the first exon . This putative SHL6 gene encodes a member of a
glycan synthase -like (GSL12 ) gene family that includes callose synthase . The β -1 ,3 -D -glucan callose is found in the cell plate of dividing cells , in pollen mother cell walls , and
pollen tubes . Callose synthase and related genes have not been previously implicated in
developmental responses to light . We also observed that 90 % of Col -0 anthers showed
high callose deposition , but shl6 mutant did not display callose deposition in the anthers .
The pollen viability in the shl6 was lower than Col -0 . The epidermal cell elongation in
shl6 hypocotyls was reduced when compared with Col -0 . Therefore , we conclude that
the mutation in light -regulated SHL6 /GSL12 was involved in the synthesis of callose as
well as light signaling . |