Map-based cloning of qBWT-c12 discovered brassinosteroid-mediated control of organ size in cotton

NAC transcription factor GbNTL9 modifies the accumulation and organization of cellulose microfibrils to enhance cotton fiber strength

INTRODUCTION

Fiber strength is a critical determinant of fiber quality, with stronger fibers being highly preferred in the cotton textile industry. However, the genetic basis and the specific regulatory mechanism underlying the formation of cotton fiber strength remain largely unknown.

OBJECTIVES

To explore fiber strength-related genes, QTL mapping, map-based cloning, and gene function verification were conducted in a backcross inbred line BS41 derived from interspecific hybridization between upland cotton and sea-island cotton.

METHODS

Upland cotton Emian22 (E22) and an interspecific backcross inbred line (BIL) BS41 were used as parents to construct secondary segregation populations for BSA and QTL mapping of fiber strength. The candidate gene GbNTL9 was identified through map-based cloning and expression analysis. The function of NTL9 was determined through transgenic experiments and cytological observations. The regulatory mechanisms of NTL9 were explored using RNA-seq, RT-qPCR, yeast two-hybrid, bimolecular fluorescence complementation, and yeast one-hybrid.

RESULTS

A major QTL for fiber strength, qFS-A11-1, was mapped to a 14.6-kb genomic region using segregating populations from E22 × BS41. GbNTL9, which encodes a NAC transcription factor, was identified as the candidate gene. Overexpression of both upland cotton genotype NTL9E22 and sea-island genotype NTL9BS41 in upland cotton enhanced fiber strength by facilitating the dense accumulation and orderly organization of cellulose microfibrils within the cell wall. Transcriptomic analysis revealed that NTL9 inhibited the expression of genes involved in secondary wall synthesis, such as CESA4, CESA7, and CESA8, thereby delaying cell wall cellulose deposition and altering the microfibril deposition pattern. NTL9 interacted with MYB6 and functioned as a downstream gene in the ethylene signaling pathway. Additionally, an effective gene marker NTL9-24 was developed to distinguish haplotypes from G. barbadense and G. hirsutum for fiber quality breeding program.

CONCLUSION

Our findings demonstrate that GbNTL9 positively regulates fiber strength through altering the microfibril deposition pattern, and provide a new insight into the molecular mechanism underlying fiber strength.

Brassinosteroids in cotton: orchestrating fiber development

Cotton cultivation spans over 30 million hectares across 85 countries and regions, with more than half participating in the global cotton textile trade. The elongated cotton fiber cell is an ideal model for studying cell elongation and understanding plant growth and development. Brassinosteroids (BRs), recognized for their role in cell elongation, offer the potential for improving cotton fiber quality and yield. Despite extensive research highlighting BR's positive impact on fiber development, a comprehensive review on this topic has been lacking. This review addresses this gap, providing a detailed analysis of the latest advancements in BR signaling and its effects on cotton fiber development. We explore the complex network of BR biosynthesis components, signaling molecules, and regulators, including crosstalk with other pathways and transcriptional control mechanisms. Additionally, we propose molecular strategies and highlight key genetic elements for optimizing BR-related genes to enhance fiber quality and yield. The review emphasizes the importance of BR homeostasis and the hormonal landscape during cotton fiber development, offering insights into targeted manipulation opportunities and challenges. This consolidation offers a comprehensive understanding of BR's multifaceted roles in fiber development, outlining a strategic approach for BR optimization in cotton fiber quality and yield.

TIP41L, a putative candidate gene conferring both seed size and boll weight, was fine-mapped in an introgression line of Gossypium hirsutum-Gossypium arboreum

QTLs for yield-related traits in tetraploid cotton have been widely mapped, but QTLs introduced from diploid species into tetraploid cotton background remain uninvolved. Here, a stable introgression line with the traits of small boll and seed on Chr. A12, IL197 derived from Gossypium hirsutum (2n = AADD = 52) × Gossypium arboreum (2n = AA = 26), was employed to construct the F₂ and F₃ secondary populations for fine-mapping QTLs of yield-related traits. QTL analysis showed eight QTLs were detected for three traits, boll weight (BW), seed index (SI, one-hundred-seed weight in g), and lint percentage, with 3.94-28.13 % of the phenotypic variance explained. Of them, a stable major QTL, q(BW + SI)-A12-1 controlling both BW and SI and covering the shortest region in Chr. A12, was further narrowed into a 60.09 kb-interval through substitution mapping. Finally, five candidate genes were detected in the interval. The qRT-PCR analysis revealed only TIP41-like family protein (TIP41L) kept up-regulated expression and significantly lower in TM-1 than that in IL197 from -1 DPA to 15 DPA during cotton boll rapid developmental stage. Therefore, TIP41L gene is speculated as the most likely candidate gene. Comparative analysis with the other four allotetraploid species showed TIP41L gene was probably diverged after the formation of allotetraploid cotton, which may be selected and swept during domestication of modern upland cotton because small boll and seed are detrimental to fibre yield of cotton. This research would lay a solid foundation for further elucidating the molecular mechanism of cotton boll and seed development.

Gene Pyramiding for Sustainable Crop Improvement against Biotic and Abiotic Stresses

Sustainable agricultural production is endangered by several ecological factors, such as drought, extreme temperatures, excessive salts, parasitic ailments, and insect pest infestation. These challenging environmental factors may have adverse effects on future agriculture production in many countries. In modern agriculture, conventional crop-breeding techniques alone are inadequate for achieving the increasing population’s food demand on a sustainable basis. The advancement of molecular genetics and related technologies are promising tools for the selection of new crop species. Gene pyramiding through marker-assisted selection (MAS) and other techniques have accelerated the development of durable resistant/tolerant lines with high accuracy in the shortest period of time for agricultural sustainability. Gene stacking has not been fully utilized for biotic stress resistance development and quality improvement in most of the major cultivated crops. This review emphasizes on gene pyramiding techniques that are being successfully deployed in modern agriculture for improving crop tolerance to biotic and abiotic stresses for sustainable crop improvement.