李文强等《Crop Journal》2022年

论文题目：Characterization of wavy root 1, an agravitropism allele, reveals the functions of OsPIN2 in fine regulation of auxin transport and distribution and in ABA biosynthesis and response in rice (Oryza sativa L.)

论文作者：Wenqiang Li ^a,1,*,Minjuan Zhang ^a,b,1, Lei Qiao ^a,c,1, Yunbo Chen ^a, Dapeng Zhang ^d,1, Xiuqing Jing ^a, Pengfei Gan ^a, Yangbin Huang ^a, Junru Gao ^a, Wenting Liu ^a, Chunhai Shi ^d, Hongchang Cui ^a,e, Haifeng Li ^c,*, Kun-Ming Chen ^a,*

论文摘要：Root system architecture is influenced by gravity. How the root senses gravity and directs its orientation, so-called gravitropism, is not only a fundamental question in plant biology but also theoretically important for genetic improvement of crop root architecture. However, the mechanism has not been elucidated in most crops. We characterized a rice agravitropism allele, wavy root 1 (war1), a loss-of-function allele in OsPIN2, which encodes an auxin efflux transporter. With loss of OsPIN2 function, war1 leads to altered root system architecture including wavy root, larger root distribution angle, and shallower root system due to the loss of gravitropic perception in root tips. In the war1 mutant, polar auxin transport was disrupted in the root tip, leading to abnormal auxin levels and disturbed auxin transport and distribution in columella cells. Amyloplast sedimentation, an important process in gravitropic sensing, was also decreased in root tip columella cells. The results indicated that OsPIN2 controls gravitropism by finely regulating auxin transport, distribution and levels, and amyloplast sedimentation in root tips. We identified a novel role of OsPIN2 in regulating ABA biosynthesis and response pathways. Loss of OsPIN2 function in the war1 resulted in increased sensitivity to ABA in seed germination, increased ABA level, changes in ABA-associated genes in roots, and decreased drought tolerance in the seedlings. These results suggest that the auxin transporter OsPIN2 not only modulates auxin transport to control root gravitropism, but also functions in ABA signaling to affect seed germination and root development, probably by mediating crosstalk between auxin and ABA pathways.

作物根系构型直接影响根的固着、支撑、吸收和转运等多方面功能。根系如何感知重力并调控其伸长方向——根向地性生长机制是植物科学研究中的一个重要基础问题，并对作物根系遗传改良具有理论研究意义。在模式植物拟南芥中大量研究表明——生长素极性运输对根向地性感知发挥重要调控作用。然而，在绝大多数作物中，根向地性生长的分子调控机制还有待阐明。该研究从水稻93-11中鉴定到一个无向地性突变体wavy root 1 (war1)，图位克隆表明其野生型基因编码生长素转运蛋白OsPIN2。OsPIN2基因功能缺失突变导致war1突变体根丧失向地性应答，进而引起根波浪状卷曲伸长、根系角度增大及深度降低等异常表型。同野生型相比，war1突变体根尖生长素极性运输受阻，导致整个根冠尤其小柱细胞区生长素浓度异常且生长素转运和分布紊乱，并引起小柱细胞内淀粉体沉淀减少，因而根尖失去向地性感知。结果表明OsPIN2通过调控根尖生长素转运和分布以及淀粉体沉淀等生理过程，进而控制根的向地性生长。此外，研究者还发现OsPIN2参与调控ABA合成和信号应答等生理过程。OsPIN2基因功能缺失导致突变体种子萌发对外源ABA超敏感，根中ABA含量升高，ABA合成和信号转导途径中相关关键基因表达改变，以及幼苗对干旱胁迫抗性降低。研究结果进一步阐明了生长素信号调控根系向地性生长并作用于ABA途径的作用机制，为定向遗传改良水稻根系构型和非生物胁迫抗性提供了新的思路。

图1 水稻war1突变体产生根系波浪状卷曲表型

文章链接：https://doi.org/10.1016/j.cj.2021.12.004