背景回顾：Soil compaction represents a major agronomic challenge, inhibiting root elongation and impacting crop yields. Roots use ethylene to sense soil compaction as the restricted air space causes this gaseous signal to accumulate around root tips. 

提出问题：Ethylene inhibits root elongation and promotes radial expansion in compacted soil, but its mechanistic basis remains unclear. 

主要发现：Here, we report that ethylene promotes abscisic acid (ABA) biosynthesis and cortical cell radial expansion. 

结果1-ABA：Rice mutants of ABA biosynthetic genes had attenuated cortical cell radial expansion in compacted soil, leading to better penetration.  

结果2-Auxin：Soil compaction-induced ethylene also up-regulates the auxin biosynthesis gene OsYUC8. Mutants lacking OsYUC8 are better able to penetrate compacted soil. The auxin influx transporter OsAUX1 is also required to mobilize auxin from the root tip to the elongation zone during a root compaction response. Moreover, osaux1 mutants penetrate compacted soil better than the wild-type roots and do not exhibit cortical cell radial expansion.

结论：We conclude that ethylene uses auxin and ABA as downstream signals to modify rice root cell elongation and radial expansion, causing root tips to swell and reducing their ability to penetrate compacted soil.

 摘 要 

土壤紧实对于农艺来说是一项重大挑战，它抑制了作物的根系伸长并影响产量。由于紧实土壤而导致一定空间中的空气受限，促进了植物激素乙烯在根尖的积累，因此植物的根组织可以通过乙烯信号来感知紧实的土壤环境。在紧实土壤中，乙烯能够抑制根的伸长并增加根的径向生长，但是具体的分子调控机制并不清楚。本文中，作者发现乙烯能够促进ABA的生物合成和皮层细胞的径向扩张。水稻ABA生物合成基因的突变会减弱其在紧实土壤中皮层细胞的径向扩张，从而导致根的穿透性更强。紧实土壤所诱导的乙烯也上调了生长素生物合成基因OsYUC8的表达。OsYUC8功能缺失突变体能够更好地穿透紧实土壤。在根对于紧实土壤的响应过程中，需要生长素内流转运蛋白OsAUX1作用于将生长素从根尖转运至伸长区。此外，osaux1突变体比野生型的根能够更好地穿透紧实土壤，并且不存在皮层细胞的径向扩展。因此，作者总结道乙烯利用生长素和ABA作为下游信号，调节水稻根细胞的伸长和径向扩张，从而导致根尖膨大并降低其穿透紧实土壤的能力。

 Malcolm Bennett