Cauliflower (
Brassica oleracea var. botrytis), which belongs to the family Brassicaceae, is characterized by an enlarged inflorescence (i.e., curd) that serves as its primary edible organ [
1]. Notably, cauliflower is cultivated globally and widely consumed as a vegetable because of its exceptional nutritional value. Its curd comprises short, thick, and fleshy stems along with an undifferentiated inflorescence meristem, making it a distinctive feature of the plant. Cauliflower curd growth and development exhibits unique reproductive characteristics that are extremely sensitive to environmental changes. This sensitivity can lead to premature flowering, formation of loose or “hairy” curds, and other developmental defects that adversely affect curd quality, potentially resulting in significant yield losses or even total crop failure. Consequently, compared with the cultivation of other commercially produced vegetables, the cultivation of cauliflower faces greater risks and challenges. Hence, the genes and associated epigenetic and physiological mechanisms regulating cauliflower responses to abiotic stresses should be identified and characterized. Elucidating these underlying mechanisms is crucial for understanding how cauliflower adapts to environmental changes. This knowledge has significant implications for breeding new varieties with enhanced stress resistance, which is essential for stabilizing yield and quality under variable environmental conditions. Developing stress-resistant varieties will mitigate production risks, while also ensuring the sustainable cultivation of cauliflower, with beneficial effects on consumer health.
Programmed cell death (PCD) is a widespread phenomenon in plants and animals [
2]. While PCD is primarily known for its role in responses to various biotic and abiotic stresses, it also plays a general role in certain aspects of plant growth and development [
3]. Apoptosis, a specific form of PCD, refers to a gene-regulated systematic process involving cellular self-destruction and is characterized by the loss of euchromatin structural information, leading to chromatin condensation and cell death [
4]. More specifically, PCD in plants generally necessitates the activation of certain genes [
5]. The Bax inhibitor-1 (
BI-1) family of highly conserved transmembrane proteins has been extensively studied regarding its contributions to cell protection, ion homeostasis regulation, and anti-apoptotic activities [
6].
BI-1 family genes encode critical inhibitors of apoptosis that are responsive to endogenous and exogenous stimuli [
7]. These genes have been thoroughly studied in terms of their effects on stress tolerance in various species. They are crucial for enhancing the tolerance of different organisms to a wide range of environmental stresses. Earlier research indicated the heterologous expression of Arabidopsis
BI-1 increases the tolerance of monocotyledonous and polycarpic plants to menadione sodium bisulfite, hydrogen peroxide, and drought-induced stress [
8,
9,
10] Under water stress conditions, the expression of
AtBI1 regulates PCD in root tips [
11]. In barley,
BI-1 is reportedly responsive to an infection by
Blumeria graminis, resulting in compromised osmotic homeostasis [
12]. Additionally, melatonin increases
BI-1 expression levels in
Medicago sativa roots under highly saline conditions [
13]. Arabidopsis contains five
BI-1 homologs, which have been designated as
LIFEGUARD 1-5 (
LFG1-5). Both
LFG1 and
LFG3 inhibit apoptosis induced by endoplasmic reticulum (ER) stress, after which they participate in the inositol-requiring enzyme 1 (IRE1) signaling pathway to enable the plant to resume normal growth [
14]. These two proteins also interact with membrane-bound progesterone receptor 3 (MAPR3) to modulate ER stress-induced apoptosis mediated by the IRE1 pathway [
14,
15,
16]. In contrast,
LFG5 inhibits apoptosis through the IRE1 signaling pathway by regulating the balance of oxidized and reduced glutathione (GSH) [
17]. Hence,
BI-1 family genes are important for plant resistance to abiotic and biotic stresses. However,
BI-1 gene families in horticultural crops have not been comprehensively investigated. More specifically, there has been relatively little research on the cauliflower
BI-1 gene family and its role in abiotic stress resistance. Among
BI-1 family genes,
LFG2, which is also known as
BRZ-INSENSITIVE-LONG HYPOCOTYLS 4 (
BIL4), encodes a protein with seven transmembrane domains. The considerable interest in this gene is due to its pivotal role in plant processes, especially responses to brassinosteroid (BR) and various abiotic stresses.
BIL4 positively regulates BR signaling by preventing the degradation of the BR receptor BRI1, thereby ensuring plants are appropriately responsive to BR, which is necessary for optimal growth and adaptations to environmental changes [
18]. A previous study showed
BIL4 is essential for maintaining cell turgor and overall stress tolerance, suggesting that it helps preserve cellular structures critical for stress tolerance [
18].
BIL4 may interact with other stress-responsive genes to enhance the ability of plants to cope with adverse environmental conditions [
19]. In our previous comparative genomic study, we identified structural variations in the
BIL4 promoter region between cauliflower and cabbage, implying that
BIL4 may differentially affect various
B. oleracea morphotypes [
20]. This raises several important questions: What are the characteristics and tissue-specific features of the
BI-1 gene family in cauliflower? How do these genes (e.g.,
BIL4) modulate cauliflower growth and development, particularly in response to abiotic stress?