Nitrogen is a crucial element for the growth and development of plants, directly affecting crop growth and yield. To investigate the physiological and molecular mechanism of nitrogen-deficiency stress, we conducted an investigation into the effects of different nitrogen levels on the growth, photosynthetic characteristics, and gene transcription levels of banana seedlings. Compared with the control group with normal nitrogen levels (NN), the height of plants receiving Reduced-N (NR), Low-N (LN), and N-Free (NF) treatments was decreased by 0.45 cm, 2.5 cm, and 3.25 cm, respectively. Their dry weight was reduced by 1.63 g, 2.99 g, and 2.88 g, respectively. Conversely, the dry weight of the underground plant part in the LN and NF treatment groups exhibited an increase of 0.13 g and 0.16 g, respectively. Regarding photosynthetic characteristics, the Specialty Products Agricultural Division (SPAD) values of the NR, LN, and NF treatments showed reductions of 15.5%, 30.4%, and 35.9%, respectively, compared with those of the control treatments. The values of maximum photosynthetic efficiency (Fv/Fm), actual photosynthetic efficiency (Y(Ⅱ)), and relative electron transfer (ETR) of the banana seedlings decreased to different degrees after NR, LN, and NF treatment, and their values were positively correlated with N levels. Gene transcription analysis showed that N transport-related proteins, including NRT1.7, NRT2.3a, NRT2.3b, and NRT2.5, were significantly up-regulated to increase the nitrogen absorption capacity of plant roots. On the other hand, various transcription factors including GRAS, MYB, and WRKY were notably up-regulated, facilitating root growth and the expanding root absorption area, thereby enhancing nitrogen uptake. Furthermore, genes associated with endogenous hormone metabolic pathways such as gibberellin (GA), strigolactone (SL), and brassinosteroids (BR) were activated in banana plants subjected to low nitrogen stress, enhancing the plant’s ability to adapt to nitrogen-deficient conditions. These findings offer valuable insights into understanding the transcriptional regulatory mechanisms governing banana responses to low nitrogen stress and breeding new varieties with improved nutrient utilization.

The TGA (TGACG motif-binding factor) transcription factors are integral to root growth and development, and are pivotal in mediating plant responses to abiotic stresses. Nonetheless, their role in the nutrient absorption processes of banana plants has not been extensively investigated. This research conducted a comprehensive analysis of the MaTGA gene family, emphasizing their physicochemical characteristics, phylogenetic relationships, gene duplication events, promoter cis-regulatory elements and protein interaction networks. Furthermore, this study investigated the expression patterns of MaTGA family members under varying nitrogen conditions. A total of 18 MaTGA members were identified within the banana genome, each encoding proteins characterized by the presence of bZIP and DOG domains. These genes exhibited an uneven distribution across eight chromosomes. Phylogenetic analysis further classified the MaTGA family into four distinct subgroups (I–IV), consisting of three, seven, three, and five members, respectively. An analysis of promoter cis-elements indicated that over 50% of the MaTGA gene family members contain hormone-responsive elements associated with abscisic acid (ABRE), ethylene (ERE), and salicylic acid (SARE), in addition to stress-responsive elements related to drought (MBS) and low temperature (LTR). Regarding gene expression, MaTGA7, MaTGA8, and MaTGA15 exhibited significantly elevated expression levels in the leaves and roots relative to other tissues. Under varying nitrogen conditions, 13 members, including MaTGA7 and MaTGA8, demonstrated the highest expression levels under reduced nitrogen (70%) treatment, followed by low nitrogen (20%) conditions, and the lowest expression levels were observed under nitrogen-deficient conditions. These findings imply that MaTGA genes may play crucial roles in enhancing nitrogen use efficiency. Protein interaction predictions suggest that MaTGA7, MaTGA8, and MaTGA15 may interact with nitrogen-related proteins, including Nitrate Transporter 2 (NRT2.1 and NRT2.2), NIN-Like Protein 7 (NLP7), and Nitrate Transporter 1.1 (NPF6.3). In summary, MaTGA7, MaTGA8, and MaTGA15 are likely involved in the processes of nitrogen absorption and utilization in bananas. The present findings establish a basis for subsequent investigations into the functional roles of MaTGA genes in augmenting nutrient use efficiency and mediating responses to abiotic stresses in banana plants.