Potassium (K) plays a crucial role in multiple physiological and developmental processes in plants. Its deficiency is a common abiotic stress that inhibits plant growth and reduces crop productivity. A better understanding of the mechanisms involved in plant responses to low K could help to improve the efficiency of K use in plants. However, such responses remain poorly characterized in fruit tree species such as pears (Pyrus sp). We analyzed the physiological and transcriptome responses of a commonly used pear rootstock, Pyrus betulaefolia, to K-deficiency stress (0 mM). Potassium deprivation resulted in apparent changes in root morphology, with short-term low-K stress resulting in rapidly enhanced root growth. Transcriptome analyses indicated that the root transcriptome was coordinately altered within 6 h after K deprivation, a process that continued until 15 d after treatment. Potassium deprivation resulted in the enhanced expression (up to 5-fold) of a putative high-affinity K⁺ transporter, PbHAK5 (Pbr037826.1), suggesting the up-regulation of mechanisms associated with K⁺ acquisition. The enhanced root growth in response to K-deficiency stress was associated with a rapid and sustained decrease in the expression of a transcription factor, PbMYB44 (Pbr015309.1), potentially involved in mediating auxin responses, and the increased expression of multiple genes associated with regulating root growth. The concentrations of several phytohormones including indoleacetic acid (IAA), ABA, ETH, gibberellin (GA₃), and jasmonic acid (JA) were higher in response to K deprivation. Furthermore, genes coding for enzymes associated with carbon metabolism such as SORBITOL DEHYDROGENASE (SDH) and SUCROSE SYNTHASE (SUS) displayed greatly enhanced expression in the roots under K deprivation, presumably indicating enhanced metabolism to meet the increased energy demands for growth and K⁺ acquisition. Together, these data suggest that K deprivation in P. betulaefolia results in the rapid re-programming of the transcriptome to enhance root growth and K⁺ acquisition. These data provide key insights into the molecular basis for understanding low-K-tolerance mechanisms in pears and in other related fruit trees and identifying potential candidates that warrant further analyses.

Cucurbita Linn. vegetables have a long history of cultivation and have been cultivated all over the world. With the increasing area of saline–alkali soil, Cucurbita Linn. is affected by salt stress, and calmodulin-binding transcription activator (CAMTA) is known for its important biological functions. Although the CAMTA gene family has been identified in several species, there is no comprehensive analysis on Cucurbita species. In this study, we analyzed the genome of Cucurbita maxima and Cucurbita moschata. Five C. moschata calmodulin-binding transcription activators (CmoCAMTAs) and six C. maxima calmodulin-binding transcription activators (CmaCAMTAs) were identified, and they were divided into three subfamilies (Subfamilies I, II, and III) based on the sequence identity of amino acids. CAMTAs from the same subfamily usually have similar exon–intron distribution and conserved domains (CG-1, TIG, IQ, and Ank_2). Chromosome localization analysis showed that CmoCAMTAs and CmaCAMTAs were unevenly distributed across four and five out of 21 chromosomes, respectively. There were a total of three duplicate gene pairs, and all of which had experienced segmental duplication events. The transcriptional profiles of CmoCAMTAs and CmaCAMTAs in roots, stems, leaves, and fruits showed that these CAMTAs have tissue specificity. Cis-acting elements analysis showed that most of CmoCAMTAs and CmaCAMTAs responded to salt stress. By analyzing the transcriptional profiles of CmoCAMTAs and CmaCAMTAs under salt stress, it was shown that both C. moschata and C. maxima shared similarities against salt tolerance and that it is likely to contribute to the development of these species. Finally, quantitative real-time polymerase chain reaction (qRT-PCR) further demonstrated the key role of CmoCAMTAs and CmaCAMTAs under salt stress. This study provided a theoretical basis for studying the function and mechanism of CAMTAs in Cucurbita Linn.

Summary: Tipburn is a common physiological disorder in leafy vegetables, significantly impairing crop growth and commercial value. It is widely recognized that Ca²⁺ deficiency is a key factor triggering tipburn; however, the functions and regulatory mechanisms of genes conferring resistance remain largely unexplored. Through transcriptomic analysis of Chinese cabbage under normal (medium calcium, MCa) and Ca²⁺‐deficient (low calcium, LCa) conditions, we observed that genes in the hormone and calcium signalling pathways exhibited significant responses to LCa stress. Among these, the cyclic nucleotide‐gated ion channel (CNGC) genes BrCNGC12 and BrCNGC16, part of the calcium signalling pathway, were notably up‐regulated and down‐regulated, respectively, under LCa stress. Silencing BrCNGC12 in Chinese cabbage improves Ca²⁺ absorption and distribution, which strengthens tipburn resistance. Conversely, under LCa stress, heterologous expression of BrCNGC16 in Arabidopsis thaliana increases resistance to tipburn, whereas partial silencing of BrCNGC16 in Chinese cabbage diminishes resistance, with both outcomes linked to altered Ca²⁺ uptake and translocation. Additionally, overexpression of BrCNGC16 in Chinese cabbage promotes Ca²⁺ uptake and translocation, thereby enhancing resistance to tipburn and mitigating oxidative damage induced by Ca²⁺ deficiency. In conclusion, BrCNGC12 and BrCNGC16 play pivotal roles in tipburn resistance in Chinese cabbage, offering novel insights into the interplay between the calcium signalling pathway and tipburn resistance.