Improved cotton yield: Can we achieve this goal by regulating the coordination of source and sink?

Abstract

Cotton is one of the major cash crops globally. It is characterized by determinate growth and multiple fruiting, which makes the source-sink contradiction more obvious. Coordination between source and sink is crucial for normal growth, yield, and quality of cotton. Numerous studies reported how the assimilate transport and distribution under varying environmental cues affected crop yields. However, less is known about the functional mechanism underlying the assimilate transport between source and sink, and how their distribution impacts cotton growth. Here, we provided an overview of the assimilate transport and distribution mechanisms , and discussed the regulatory mechanisms involved in source-sink balance in relation to cotton yield. Therefore, this review enriched our knowledge of the regulatory mechanism involved in source-sink relationship for improved cotton yield.

Keywords: coordination; cotton; crop yield; regulation mechanism; source–sink relationship.

Figure 1

Schematic illustration of the source to sink carbon transport. (A) Sucrose is translocated from the mesophyll cell to the companion cells, and finally to the sieve elements of the collection phloem (CP) under a high concentration gradient. (B) Sucrose is moved from the collection phloem (CP) to the transport phloem (TP) and finally reaches the release phloem (RP) via the activities of sucrose transporters, including SWEET and SUTs. (C) The release phloem unloads the sucrose at the sink organ under a low concentration gradient for fiber development. Chao et al. (2020) revealed that GhSUT11 is expressed in the source and sink organ, but its function is unknown. The crew also found that GhSUT6 and GhSUT11 were expressed in the sink organ, but the function of these genes in sucrose transport is unclear (Chao et al., 2020). The genes regulating sucrose transport from leaf to mesophyll cells and from mesophyll cells to the companion cells are yet to be identified. GhSUT1-L2 is involved in the phloem transport of sucrose from the leaf; however, the gene responsible for phloem unloading is unknown. Recently, Yu et al. (2023) showed that GhSUT9 expressed in the petal (sink organ) enhances starch and sucrose content in the anther. However, GhSUT1 and ZmSUT1 promote cotton fiber elongation (Guo et al., 2017; Ding et al., 2019).

Figure 2

Future prospects of studying the source–sink coordination in cotton. The upper part of the picture (in the dotted box in the gray background) shows several solutions for modulating the source–sink to improve cotton production. The lower part of the picture indicates the main breakthrough steps to predict the regulatory mechanism of the source–sink relationship in cotton, which is as follows: (1) screening and identification of the key genes and metabolites affecting sugar transport and distribution; (2) screening and identification of key genes and metabolites affecting the nitrogen use efficiency (NUE); (3) elucidating the internal mechanism of how plant hormones participate in the regulatory network of the source–sink relationship. C, carbon; N, nitrogen; Suc, sucrose; SUTs, sucrose transporters; SWEETs, SUGAR WILL EVENTUALLY BE EXPORTED TRANSPORTERS; NUE, nitrogen use efficiency; NRTs, nitrate transporters; NLPs, nodule-inception-like proteins; GA, gibberellic acid; CK, cytokinin; BR, brassinosteroid; ABA, abscisic acid; IAA, auxin/indoleacetic acid; ETH, ethylene.