Nitrogen Recycling System Analyzed by Molecular Physiology together with QTL Analysis in Rice

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A quantitative trait locus (QTL) associated with the protein content of cytosolic glutamine synthetase (GS1 ; EC 6.3.1.2) in senescing leaves, panicle number and panicle weight was characterized in rice (Oryza sativa L.). A nearly isogenic line (NIL), C-22, developed by marker-assisted selection was grown under different nitrogen levels in a greenhouse and in a paddy field. C-22 had a small segment (approximately 50 cM) substituted from the Kasalath chromosome in chromosome 2 on a Koshihikari genetic background. C-22 showed a 12-37% lower content of GS1 protein in leaf blades than Koshihikari, which was in good agreement with a QTL region positively affected by the japonica chromosome. At an early vegetative stage, C-22 had more active tillers than Koshihikari in the greenhouse. At the reproductive stage, both panicle number and total panicle weight of C-22 were significantly higher than those of Koshihikari, particularly when grown with a low-nitrogen condition. These traits of C-22 were further confirmed in a paddy field. Thus, development of tillers was positively affected by the Kasalath chromosome at an early vegetative stage, which increased the panicle number and panicle weight at the mature stage in C-22. These data indicate that the target QTL (Pnn1 ; panicle number 1) is important in the development of tillers and panicles in rice. Pnn1 was delimited at the 6.7 cM region, demonstrating that developing tiller formation in the 2nd axil (RDT ; ratio of developing tillers formation in the 2nd axil) was determined using substituted lines. This QTL region has been successively narrowed down to 23 kb using various substituted lines of Kasalath chromosome.Physiological function of GS1 ; 1 has been investigated using knock-out mutants of GS1 ; 1 gene and this result will be published in Plant Journal. In addition, function of PII-like protein that would be expected to be involved in the Gln signaling has also been published.