Lack of Cytosolic Glutamine Synthetase1;2 Activity Reduces Nitrogen-Dependent Biosynthesis of Cytokinin Required for Axillary Bud Outgrowth in Rice Seedlings
Lack of Cytosolic Glutamine Synthetase1;2 Activity Reduces Nitrogen-Dependent Biosynthesis of Cytokinin Required for Axillary Bud Outgrowth in Rice Seedlings
复制标题
DOI：
10.1093/pcp/pcx022
复制
发表时间：
2017-04-01
影响因子：
4.9
通讯作者：
Hayakawa, Toshihiko
中科院分区：
文献类型：
--
作者：
Ohashi, Miwa;Ishiyama, Keiki;Hayakawa, Toshihiko
在突变的水稻幼苗中，取消胞质谷氨酰胺合成酶1；2(GS1；2)活性的突变会损害根和地上部将铵同化为谷氨酰胺，并严重减少腋芽的生长(分蘖)。虽然gs1；2突变体的表型不依赖于抑制分蘖的三七内酯，但它也显示了谷氨酰胺或相关代谢物应答的细胞分裂素(CK)的生物合成，从而促进了分蘖。在这里，我们研究了GS1；2与分蘖过程中CK生物合成的关系，重点研究了GS1；2突变体的地上部以及顶芽和腋芽分生组织。尽管有足够的铵供应，但突变体地上部的前体CK含量和氨同化为谷氨酰胺的能力都有所下降。由自身启动子驱动的OsGS1；2基因的重新表达使前体CK含量和氨同化恢复到野生型水平。在地上部，谷氨酰胺反应的磷酸腺苷-异戊烯基转移酶4(OsIPT4)是合成CK的IPT的主要同源基因，该酶在水稻根中也占主导地位。在GS1；2突变体中，与腋芽维管系统相连的结节维管中韧皮部伴胞中的OsIPT4的细胞特异性表达也减少。在突变体的腋芽分生组织中，作为活性CKS局部指标的CK-响应型A反应调节基因的表达也被取消。这些结果表明，缺乏GS1；2活性降低了CK生物合成所需的谷氨酰胺或相关代谢物的水平，导致分蘖所必需的腋芽分生组织中活性CK的缺乏。
A mutation abolishing cytosolic glutamine synthetase1; 2 (GS1;2) activity impairs assimilation of ammonium into glutamine in both roots and basal portions of shoots, and severely decreases axillary bud outgrowth (tillering) in mutant rice seedlings. Although the gs1;2 mutant phenotype is independent of strigolactone, which inhibits tillering, it also demonstrates glutamine-or related metabolite-responsive biosynthesis of cytokinin (CK), which promotes tillering. Here, we examined the connection between GS1;2 and CK biosynthesis during tillering, focusing on basal portions of the shoots as well as apical and axillary bud meristems in the gs1;2 mutant. Despite a sufficient ammonium supply, decreases in precursor CK contents and a decrease in ammonium assimilation into glutamine were observed in basal portions of mutant shoots. Reintroducing expression of OsGS1;2 cDNA driven by its own promoter restored precursor CK contents and ammonium assimilation to wild-type levels. In basal portions of the shoots, glutamine-responsive adenosine phosphate-isopentenyltransferase4 (OsIPT4), which is also predominant in rice roots, was the predominant isogene for IPT, which synthesizes CK. Cell-specific expression of OsIPT4 in phloem companion cells in nodal vascular anastomoses connected to the axillary bud vasculature also decreased in the gs1;2 mutant. Expression of CK-responsive type-A response regulator genes as local indicators of active CKs was also abolished in the axillary bud meristem of the mutant. These results suggest that the lack of GS1;2 activity decreased levels of glutamine or a related metabolite required for CK biosynthesis, causing a deficiency in active CK in the axillary bud meristem necessary for tillering.