Rajendran Sujeevan, Kim Chul Min
Department of Horticulture Industry, Wonkwang University, Iksan 54538, Republic of Korea.
Plants (Basel). 2022 Dec 19;11(24):3580. doi: 10.3390/plants11243580.
Root hairs play crucial roles in the roots, including nutrient uptake, water assimilation, and anchorage with soil, along with supporting rhizospheric microorganisms. In rice, ammonia uptake is mediated by a specialized ammonium transporter (AMT). AMT1;1, AMT1;2, and AMT1;3 have been extensively studied in relation to nitrogen signaling. Cellulose synthase-like D1 (CSLD1) is essential for cell expansion and is highly specific to root hair cells. csld1 mutants showed successful initiation but failed to elongate. However, when nitrogen was depleted, csld1 root hairs resumed elongation. Further experiments revealed that in the presence of ammonium (NH4+), csld1 roots failed to elongate. csld1 elongated normally in the presence of nitrate (NO3−). Expression analysis showed an increase in root hair-specific AMT1;2 expression in csld1. CSLD1 was positively co-expressed with AMT1;2 changing nitrogen concentration in the growth media. CSLD1 showed increased expression in the presence of both ammonium and nitrate. Methylammonium (MeA) treatment of CSLD1 overexpression lines suggests that CSLD1 does not directly participate in nitrogen transport. Further studies on the root hair elongation mutant sndp1 showed that nitrogen assimilation is unlikely to depend on root hair length. Therefore, these results suggest that CSLD1 is closely involved in nitrogen-dependent root hair elongation and regulation of AMT1;2 expression in rice roots.
根毛在根部发挥着关键作用，包括养分吸收、水分同化以及与土壤的固着，同时还支持根际微生物。在水稻中，氨的吸收由一种特殊的铵转运蛋白（AMT）介导。AMT1;1、AMT1;2和AMT1;3已针对氮信号传导进行了广泛研究。类纤维素合酶D1（CSLD1）对细胞扩展至关重要，且高度特异地存在于根毛细胞中。csld1突变体根毛起始成功，但无法伸长。然而，当氮缺乏时，csld1根毛恢复伸长。进一步实验表明，在铵（NH4+）存在的情况下，csld1根无法伸长。在硝酸盐（NO3−）存在时，csld1根正常伸长。表达分析显示，csld1中根毛特异性AMT1;2的表达增加。CSLD1与AMT1;2呈正共表达，且生长培养基中的氮浓度发生变化。在铵和硝酸盐同时存在的情况下，CSLD1的表达均增加。对CSLD1过表达系进行甲铵（MeA）处理表明，CSLD1不直接参与氮转运。对根毛伸长突变体sndp1的进一步研究表明，氮同化不太可能依赖于根毛长度。因此，这些结果表明，CSLD1密切参与水稻根中依赖氮的根毛伸长以及AMT1;2表达的调控。
