Bulliform cells are large, thin-walled and highly vacuolated cells, and play an important role in controlling leaf rolling in response to drought and high temperature. However, the molecular mechanisms regulating bulliform cell development have not been well documented. Here, we report isolation and characterisation of a rice leaf-rolling mutant, named shallot-like 2 (sll2). The sll2 plants exhibit adaxially rolled leaves, starting from the sixth leaf stage, accompanied by increased photosynthesis and reduced plant height and tiller number. Histological analyses showed shrinkage of bulliform cells, resulting in inward-curved leaves. The mutant is recessive and revertible at a rate of 9%. The leaf rolling is caused by a T-DNA insertion. Cloning of the insertion using TAIL-PCR revealed that the T-DNA was inserted in the promoter region of LOC_Os07 g38664. Unexpectedly, the enhanced expression of LOC_Os07 g38664 by the 35S enhancer in the T-DNA is not responsible for the leaf rolling phenotype. Further, the enhancer also exerted a long-distance effect, including up-regulation of several bulliform cell-related genes. sll2 suppressed the outward leaf rolling of oul1 in the sll2oul1 double mutant. We conclude that leaf rolling in sll2 could be a result of the combined effect of multi-genes, implying a complex network in regulation of bulliform cell development.
A cDNA sequence OsMT3 was initially isolated from the subtractive cDNA library of ammonium-fed rice (Oryza sativa L.) leaves, which was further confirmed by Northern blot to be highly ammonium-up-regulated as compared to nitrate. Its full-length cDNA was cloned by RT-PCR, and in silico analysis reveals that the cDNA includes an open reading frame of 186 bp and encodes a rice metallothionein type 3 peptide. Northern blotting analysis showed that OsMT3 gene predominantly expressed in rice leaves, weakly in stems, and barely in buds and roots. The gene transcripts in leaves were significantly induced by polyethylene glycol (PEG), low temperature, NaCl and Cu 2+ , but not by Pb 2+ . Activities of three anti-oxidative enzymes (superoxide dismutase, catalase and peroxidases) and two nonenzymic antioxidants (reduced ascorbate and reduced glutathione) little differed in ammonium-and nitrate-fed rice leaves, indicating that the induced OsMT3 expression was not mediated by ammonium-elicited oxidative signals.
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