College of Agriculture, Nanjing Agricultural University, Nanjing, China.
Jinhua Academy, Zhejiang Chinese Medical University, Jinhua, China.
J Exp Bot. 2024 Jun 7;75(11):3579-3595. doi: 10.1093/jxb/erae108.
The potential mechanisms by which drought restricts cotton fiber cell wall synthesis and fiber strength are still not fully understood. Herein, drought experiments were conducted using two cultivars of upland cotton (Gossypium hirsutum), Dexiamian 1 (drought-tolerant) and Yuzaomian 9110 (drought-sensitive). Results showed that drought notably reduced sucrose efflux from cottonseed coats to fibers by down-regulating the expression of GhSWEET10 and GhSWEET15 in outer cottonseed coats, leading to enhanced sucrose accumulation in cottonseed coats but decreased sucrose accumulation in fibers. Within cotton fibers, drought restricted the hydrolysis of sucrose to uridine-5'-diphosphoglucose by suppressing sucrose synthase activity, and drought favored the conversion of uridine-5'-diphosphoglucose to β-1,3-glucan rather than cellulose by up-regulating GhCALS5. Hence, cellulose content was reduced, which was the main reason for the decreased fiber strength under drought. Moreover, drought promoted lignin synthesis by up-regulating the expression of Gh4CL4, GhPAL9, GhCCR5, GhCAD11, and GhCOMT6, which partly offset the negative influence of reduced cellulose content on fiber strength. Compared with Yuzaomian 9110, the drought-tolerance of Dexiamian 1 was evidenced by the following under drought conditions: (i) greater sucrose flow from seedcoat to fiber, (ii) less β-1,3-glucan accumulation, and (iii) more lignin biosynthesis. Overall, this study provides new insights into the mechanism of reduced cotton fiber strength induced by drought.
干旱限制棉花纤维细胞壁合成和纤维强度的潜在机制仍未完全阐明。本研究利用两个陆地棉品种（Gossypium hirsutum）德海 1 号（耐旱）和豫早棉 9110（干旱敏感）进行干旱实验。结果表明，干旱通过下调外种皮中 GhSWEET10 和 GhSWEET15 的表达，显著减少了棉籽向纤维中蔗糖的外排，导致棉籽中蔗糖积累增加，而纤维中蔗糖积累减少。在棉花纤维内，干旱通过抑制蔗糖合酶活性抑制蔗糖水解为尿苷-5′-二磷酸葡萄糖，干旱有利于尿苷-5′-二磷酸葡萄糖向β-1,3-葡聚糖而不是纤维素的转化，通过上调 GhCALS5。因此，纤维素含量减少，是干旱下纤维强度降低的主要原因。此外，干旱通过上调 Gh4CL4、GhPAL9、GhCCR5、GhCAD11 和 GhCOMT6 的表达促进木质素合成，部分抵消了纤维素含量降低对纤维强度的负面影响。与豫早棉 9110 相比，德海 1 号在干旱条件下具有更强的耐旱性：（i）种子到纤维的蔗糖流量更大，（ii）β-1,3-葡聚糖积累更少，（iii）木质素生物合成更多。总之，本研究为干旱导致棉花纤维强度降低的机制提供了新的见解。
